In 1990, a series of brutal attacks on elderly victims occurred in Goldsboro,
North Carolina, by an unknown individual dubbed the "Night Stalker."
one such attack in March, an elderly woman was brutally raped and almost
murdered. Her daughter's early arrival home was the only thing that saved
woman's life. The suspect fled, leaving behind materials intended to burn
residence and the victim in an attempt to conceal the crime. In July 1990,
another elderly woman was brutally raped and murdered in her home. Three
months later, a third elderly woman was raped and stabbed to death. Her
husband was also murdered. Their house was burned in an attempt to cover
the crime, but fire/rescue personnel pulled the bodies from the house
was engulfed in flames.
When DNA analysis was conducted on biological evidence collected from
vaginal swabs from each victim, authorities concluded that the same perpetrator
had committed all three crimes. However, there was no suspect.
For 10 years, both the Goldsboro Police Department and the crime laboratory
refused to forget about these cases. With funding from the National Institute
Justice, the crime laboratory retested the biological evidence in all
with newer DNA technology and entered the DNA profiles into North
Carolina's DNA database. This would allow the DNA profile developed from
the crime scene evidence to be compared to thousands of convicted offender
profiles already in the database.
In April 2001, a "cold hit" was made to the perpetrator's convicted
DNA profile in the database. The perpetrator had been convicted of shooting
into an occupied dwelling, an offense that requires inclusion in the North
Carolina DNA database. The suspect was brought into custody for questioning
and was served with a search warrant to obtain a sample of his blood.
sample was analyzed and compared to the crime scene evidence, thereby
confirming the DNA database match. When confronted with the DNA
evidence, the suspect confessed to all three crimes.
Mark Nelson, special agent in charge of the North Carolina State Crime
Laboratory, said, "Even though these terrible crimes occurred more
years ago, we never gave up hope of solving them one day."
Every law enforcement department throughout the country has unsolved cases
that could be solved through recent advancements in DNA technology. Today,
investigators who understand which evidence may yield a DNA profile can
identify a suspect in ways previously seen only on television. Evidence
to the naked eye can be the key to solving a residential burglary, sexual
or murder. The saliva on the stamp of a stalker's threatening letter,
perspiration on a rapist's mask, or the skin cells shed on the ligature
strangled child may hold the key to solving a crime.
In Austin, Texas, for example, an investigator knowledgeable about DNA
technology was able to solve the rape of a local college student. Having
about the potential for obtaining DNA evidence from the ligature used
strangle a victim, the investigator requested DNA testing on the phone
used to choke the victim in his case. He realized that in the course of
someone, enough force and friction is applied to the rope or cord that
perpetrator's skins cells may rub off his hands and be left on the ligature.
The investigator's request paid off in an unanticipated way. In spite
attacker's attempt to avoid identification through DNA evidence by wearing
both a condom and rubber gloves, a reliable DNA profile was developed
the evidence. During the struggle, the attacker was forced to use one
hold the victim down, leaving only one hand to pull the phone cord tight.
attacker had to grab the remaining end of the cord with his mouth, thereby
depositing his saliva on the cord. Although the developed profile came
saliva rather than skin, DNA not only solved the case in Austin, but also
the perpetrator to a similar sexual assault in Waco.
Without the investigator's understanding of DNA technology and where DNA
might be found, the case may have gone unsolved. The successful review
investigation of unsolved cases require the same basic elements as the
investigation of new cases: cooperation among law enforcement, the crime
laboratory, and the prosecutor's office. Investigators should be aware
technological advances in DNA testing that may yield profiles where previous
testing was not performed or was unsuccessful. The crime laboratory can
essential to the preliminary review of unsolved cases, for example, by
investigators with laboratory reports from previous testing and consultation
regarding the investigative value of new DNA analysis techniques and DNA
database search capabilities. Additionally, the prosecutor's office should
involved as soon as a case is reopened so that legal issues are addressed
appropriately. It is also extremely important that case reconstruction
the victim or victim's family and the importance of finality to closing
Although DNA is not the only forensic tool available for the investigation
unsolved cases, advancements in DNA testing and the success of DNA
database systems have inspired law enforcement agencies throughout the
country to reevaluate cases previously thought unsolvable. The purpose
report is to provide law enforcement with a practical resource for the
old, cold, or unsolved cases that may be solved through DNA technology
DNA databases. "The Long and Short of DNA" and "How Can
Databases Aid Investigations?" will educate the reader about the
technology of DNA testing and DNA databases. "Practical Considerations"
provides important background information on legal and practical
considerations regarding the application of DNA technology to old, cold,
unsolved cases. Finally, a step-by-step process is provided to help investigators
select cases that would most likely be solved with DNA evidence. As
investigators advance through this process, they should also keep in mind
array of other technology advancements, such as improved ballistics and
fingerprint databases, that may benefit their investigation.
Advancements in DNA technology
Advancements in DNA analysis, together with computer technology and the
Combined DNA Index System (CODIS), have created a powerful
crimefighting tool for law enforcement. CODIS is a computer network that
connects forensic DNA laboratories at the local, State, and national levels.
DNA database systems that use CODIS contain two main criminal indexes
a missing persons index. When a DNA profile is developed from crime scene
evidence and entered into the forensic (crime scene) index of CODIS, the
database software searches thousands of convicted offender DNA profiles
(contained in the offender index) of individuals convicted of offenses
rape and murder. Similar to the Automated Fingerprint Identification System
(AFIS), CODIS can aid investigations by efficiently comparing a DNA profile
generated from biological evidence left at a crime scene against convicted
offender DNA profiles and forensic evidence from other cases contained
CODIS. CODIS can also aid investigations by searching the missing persons
index, which contains DNA profiles of unidentified remains and DNA profiles
of relatives of those who are missing. Because of the recidivistic nature
violent offenders, the power of a DNA database system is evident not only
the success of solving crimes previously thought unsolvable, but perhaps
importantly, through the prevention of crime.
When properly documented, collected, and stored, biological evidence can
analyzed to produce a reliable DNA profile years, even decades, after
collected. Just as evidence collected from a crime that occurred yesterday
be analyzed for DNA, today evidence from an old rape kit, bloody shirt,
stained bedclothes may contain a valuable DNA profile. These new analysis
techniques, in combination with an evolving database system, make a powerful
argument for the reevaluation of unsolved crimes for potential DNA evidence.
Knowledgeable law enforcement officers are taking advantage of powerful
DNA analysis techniques by investigating crime scenes with a keener eye
toward biological evidence. The same new approach being applied to crime
scene processing and current case investigation can be applied to older
unsolved cases. Law enforcement agencies across the country are establishing
cold-case squads to systematically review old cases for DNA and other
leads. This report will serve as a resource to assist law enforcement
maximizing the potential of DNA evidence in unsolved cases by covering
basics of DNA analysis and its application to forensic casework. The report
will also demonstrate how DNA database systems, advancing technology,
cooperative efforts can enhance unsolved case investigative techniques.
Advancements in DNA technology have led to significant changes in many
States' statutes, which may affect the manner in which unsolved cases
investigated, filed, and prosecuted. Advancements in the technology have
so significant that laws are being created, amended, and even repealed
advantage of its ability to identify and convict the guilty and exonerate
innocent. Laws regarding DNA admissibility in court, its use in postconviction
appeals, the creation and expansion of databases, and the extension or
elimination of statutes of limitation are examples of the quickly evolving
of DNA on the criminal justice system. Given the legal changes occurring
throughout the country, constant contact and consultation with the local
prosecutor is critical not only for the investigation of older cases but
cases in which DNA may be relevant evidence.
Statutes of limitation
Statutes of limitation may be one of the most difficult issues to overcome
examining older cases. Statutes of limitation establish time limits under
criminal charges can be filed for a particular offense. These statutes
in the protection of individuals from the use of evidence that becomes
reliable over time. For example, witnesses' memories fade as time goes
However, although some evidence, such as eyewitness accounts, can lose
credibility over time, DNA evidence has the power to determine truth 10,
even 20 years after an offense is committed. States are beginning to realize
the reliability of DNA technology may necessitate the reevaluation of
limitation in the filing of cases.
The use of DNA evidence and convicted offender DNA databases has
expanded significantly since the first U.S. DNA database was created in
Although State and local DNA databases established in the early 1990s
contained only DNA profiles from convicted murderers and sex offenders,
undeniable success of DNA databases has resulted in a national trend toward
database expansion. All States require at least some convicted offenders
provide a DNA sample to be collected for DNA profiling and, in 2000, the
Federal Government began requiring certain offenders convicted of Federal
military crimes to also provide a DNA sample for the criminal DNA database.
Recognizing that the effectiveness of the DNA database relies on the volume
data contained in both the forensic index (crime scene samples) and the
convicted offender index of CODIS, many States are changing their database
statutes to include less violent criminals. Many States are enacting legislation
require all convicted felons to submit a DNA profile to the State database.
tendency for States to include all convicted felons in their databases
dramatically increases the number of convicted offender DNA profiles against
which forensic DNA evidence can be compared, thus making the database
system a more powerful tool for law enforcement.
New legal approaches
DNA technology and DNA databases have encouraged the development of
new approaches to old cases. One such approach is the filing of charges
"John Doe" warrant. These warrants are based on the unique DNA
obtained from the analysis of unsolved crime scene evidence. Although
Doe warrants are traditionally filed based on the physical description
or alias of
an unnamed suspect, investigators and prosecutors are now filing charges
the suspect's DNA profile as the identifier. This innovative approach
allowed charges to be filed that toll and permit old cases to be prosecuted
when the person matching the John Doe DNA profile is identified. John
DNA warrants are one way to permit cases to remain active, allowing them
chance to be solved through the DNA database in the future.
The Long and Short of DNADNA is the fundamental building block for an
individual's entire genetic
makeup. It is a component of virtually every cell in the human body, and
person's DNA is the same in every cell. That is, the DNA in a person's
the same as the DNA in his skin cells, saliva, and other biological material.
DNA analysis is a powerful tool because each person's DNA is unique (with
the exception of identical twins). Therefore, DNA evidence collected from
crime scene can implicate or eliminate a suspect, similar to the use of
fingerprints. It also can analyze unidentified remains through comparisons
DNA from relatives. Additionally, when evidence from one crime scene is
compared with evidence from another using CODIS, those crime scenes can
be linked to the same perpetrator locally, statewide, and nationally.
DNA is also a powerful tool because when biological evidence from crime
scenes is collected and stored properly, forensically valuable DNA can
found on evidence that may be decades old. Therefore, old cases that were
previously thought unsolvable may contain valuable DNA evidence capable
identifying the perpetrator.
Similar to fingerprints
DNA is often compared with fingerprints in the way matches are determined.
When using either DNA or fingerprints to identify a suspect, the evidence
collected from the crime scene is compared with a "known" standard.
identifying features are the same, the DNA or fingerprint can be determined
be a match. However, if identifying features of the DNA profile or fingerprint
are different from the known standard, it can be determined that it did
from that known individual.
DNA technology advancements
Recent advancements in DNA technology have improved law enforcement's
ability to use DNA to solve old cases. Original forensic applications
analysis were developed using a technology called restriction fragment
polymorphism (RFLP). Although very old cases (more than 10 years) may
have had RFLP analysis done, this kind of DNA testing may have been
attempted on more recent unsolved cases. However, because RFLP analysis
required a relatively large quantity of DNA, testing may not have been
successful. Similarly, biological evidence deemed insufficient in size
may not have been previously submitted for testing. Also, if a biological
was degraded by environmental factors such as dirt or mold, RFLP analysis
may have been unsuccessful at yielding a result. Newer technologies could
be successful in obtaining results.
Newer DNA analysis techniques enable laboratories to develop profiles
biological evidence invisible to the naked eye, such as skin cells left
or weapons. Unsolved cases should be evaluated by investigating both
traditional and nontraditional sources of DNA. Valuable DNA evidence might
be available that previously went undetected in the original investigation.
If biological evidence is available for testing or retesting in unsolved
investigations, it is important that law enforcement and the crime laboratory
work together to review evidence. Logistical issues regarding access to
cost of DNA analysis will be a factor, as well as issues that relate to
discriminating power of each technology and that might affect the outcome
the results. Laboratory personnel can also provide a valuable perspective
which evidence might yield valuable and probative DNA results. Finally,
previously tested biological evidence produced a DNA profile but excluded
original suspect, revisiting those "exclusion" cases in the
context of comparing
them with DNA databases might prove to be very valuable to solving old
PCR (polymerase chain reaction) enhances DNA analysis and has enabled
laboratories to develop DNA profiles from extremely small samples of
biological evidence. The PCR technique replicates exact copies of DNA
contained in a biological evidence sample without affecting the original,
like a copy machine. RFLP analysis requires a biological sample about
of a quarter, but PCR can be used to reproduce millions of copies of the
contained in a few skin cells. Since PCR analysis requires only a minute
of DNA, it can enable the laboratory to analyze highly degraded evidence
DNA. On the other hand, because the sensitive PCR technique replicates
and all of the DNA contained in an evidence sample, greater attention
contamination issues is necessary when identifying, collecting, and preserving
DNA evidence. These factors may be particularly important in the evaluation
unsolved cases in which evidence might have been improperly collected
Short tandem repeat (STR) technology is a forensic analysis that evaluates
specific regions (loci) that are found on nuclear DNA. The variable
(polymorphic) nature of the STR regions that are analyzed for forensic
intensifies the discrimination between one DNA profile and another. For
example, the likelihood that any two individuals (except identical twins)
have the same 13-loci DNA profile can be as high as 1 in 1 billion or
The Federal Bureau of Investigation (FBI) has chosen 13 specific STR loci
serve as the standard for CODIS. The purpose of establishing a core set
STR loci is to ensure that all forensic laboratories can establish uniform
databases and, more importantly, share valuable forensic information.
forensic or convicted offender CODIS index is to be used in the investigative
stages of unsolved cases, DNA profiles must be generated by using STR
technology and the specific 13 core STR loci selected by the FBI.
Mitochondrial DNA analysis
Mitochondrial DNA (mtDNA) analysis allows forensic laboratories to develop
DNA profiles from evidence that may not be suitable for RFLP or STR
analysis. While RFLP and PCR techniques analyze DNA extracted from the
nucleus of a cell, mtDNA technology analyzes DNA found in a different
the cell, the mitochondrion (see exhibit 1). Old remains and evidence
nucleated cells--such as hair shafts, bones, and teeth--that are unamenable
STR and RFLP testing may yield results if mtDNA analysis is performed.
this reason, mtDNA testing can be very valuable to the investigation of
unsolved case. For example, a cold case log may show that biological evidence
in the form of blood, semen, and hair was collected in a particular case,
all were improperly stored for a long period of time. Although PCR analysis
sometimes enables the crime laboratory to generate a DNA profile from
degraded evidence, it is possible that the blood and semen would be so
degraded that nuclear DNA analysis would not yield a DNA profile. However,
the hair shaft could be subjected to mtDNA analysis and thus be the key
solving the case. Finally, it is important to note that all maternal relatives
example, a person's mother or maternal grandmother) have identical mtDNA.
This enables unidentified remains to be analyzed and compared to the mtDNA
profile of any maternal relative for the purpose of aiding missing persons
unidentified remains investigations. Although mtDNA analysis can be very
valuable to the investigation of criminal cases, laboratory personnel
always be involved in the process.
Several genetic markers have been identified on the Y chromosome that
used in forensic applications. Y-chromosome markers target only the male
fraction of a biological sample. Therefore, this technique can be very
the laboratory detects complex mixtures (multiple male contributors) within
biological evidence sample. Because the Y chromosome is transmitted directly
from a father to all of his sons, it can also be used to trace family
among males. Advancements in Y-chromosome testing may eventually eliminate
the need for laboratories to extract and separate semen and vaginal cells
example, from a vaginal swab of a rape kit) prior to analysis.
Cooperative efforts with the crime laboratory are essential to deciding
analysis methods will be most valuable in a particular case. It is important
note, however, that while RFLP and mtDNA testing may be valuable to the
investigation of an old case, current DNA databases are being populated
DNA profiles that are generated using STR analysis. RFLP and mtDNA
profiles are not compatible with the convicted offender or forensic indexes
How Can DNA Databases Aid Investigations?
The development and expansion of databases that contain DNA profiles at
local, State, and national levels have greatly enhanced law enforcement's
to solve cold cases with DNA. Convicted offender databases store hundreds
thousands of potential suspect DNA profiles, against which DNA profiles
developed from crime scene evidence can be compared.
Given the recidivistic nature of many crimes, such as sexual assault and
burglary, a likelihood exists that the individual who committed the crime
investigated was convicted of a similar crime and already has his or her
profile in a DNA database that can be searched by CODIS. Moreover,
CODIS also permits the cross-comparison of DNA profiles developed from
biological evidence found at crime scenes. Even if a perpetrator is not
through the database, crimes may be linked to each other, thereby aiding
investigation, which may eventually lead to the identification of a suspect.
What is CODIS?
CODIS is a computer software program that operates local, State, and national
databases of DNA profiles from convicted offenders, unsolved crime scene
evidence, and missing persons. Every State in the Nation has a statutory
provision for the establishment of a DNA database that allows for the
of DNA profiles from offenders convicted of particular crimes. CODIS
software enables State, local, and national law enforcement crime laboratories
to compare DNA profiles electronically, thereby linking serial crimes
other and identifying suspects by matching DNA profiles from crime scenes
with profiles from convicted offenders. The success of CODIS is demonstrated
by the thousands of matches that have linked serial cases to each other
cases that have been solved by matching crime scene evidence to known
The missing persons index consists of the unidentified persons index and
reference index. The unidentified persons index contains DNA profiles
recovered remains, such as bone, teeth, or hair. The reference index contains
DNA profiles from related individuals of missing persons so that they
periodically compared to the unidentified persons index. All samples for
index are typed using mtDNA and STR DNA analysis (if possible) to maximize
the power of advancing technology.
How does CODIS work?
CODIS uses two indexes to generate investigative leads in crimes for which
biological evidence is recovered from a crime scene. The convicted offender
index contains DNA profiles of individuals convicted of certain crimes
from certain misdemeanors to sexual assault and murder. Each State has
different "qualifying offenses" for which persons convicted
of them must submit
a biological sample for inclusion in the DNA database. The forensic index
contains DNA profiles obtained from crime scene evidence, such as semen,
saliva, or blood. CODIS uses computer software to automatically search
across these indexes for a potential match.
A match made between profiles in the forensic index can link crime scenes
each other, possibly identifying serial offenders. Based on these "forensic
police in multiple jurisdictions or States can coordinate their respective
investigations and share leads they have developed independent of each
Matches made between the forensic and convicted offender indexes can
provide investigators with the identity of a suspect(s). It is important
to note that
if an "offender hit" is obtained, that information typically
is used as probable
cause to obtain a new DNA sample from that suspect so the match can be
confirmed by the crime laboratory before an arrest is made.
LDIS, SDIS, and NDIS
CODIS is implemented as a distributed database with three hierarchical
(or tiers)--local, State, and national. All three levels contain forensic
convicted offender indexes and a population file (used to generate statistics).
The hierarchical design provides State and local laboratories with the
to configure CODIS to meet their specific legislative and technical needs.
A description of the three CODIS tiers follows (see exhibit 2).
Local. Typically, the Local DNA Index System
(LDIS) installed at crime
laboratories is operated by police departments or sheriffs' offices. DNA
originated at the local level can be transmitted to the State and national
State. Each State has a designated laboratory
that operates the State DNA
Index System (SDIS). SDIS allows local laboratories within that State
compare DNA profiles. SDIS also is the communication path between the
and national tiers. SDIS is typically operated by the agency responsible
implementing and monitoring compliance with the State's convicted offender
National. The National DNA Index System (NDIS) is the highest
level of the
CODIS hierarchy and enables qualified State laboratories that are actively
participating in CODIS to compare DNA profiles. NDIS is maintained by
FBI under the authority of the DNA Identification Act of 1994.
Limitations of using the DNA database
The more data contained in the forensic and offender indexes of CODIS,
more powerful a tool it becomes for law enforcement, especially in its
application to unsolved case investigation. However, because many jurisdictions
are in the process of developing and populating their DNA databases,
convicted offender and forensic casework backlogs have been created over
time and continue to grow for several reasons. First, as States recognize
crime-solving potential of DNA databases, they continue to expand the
of their convicted offender legislation, which increases the number of
be collected and analyzed by the DNA laboratory. As a result, more than
million uncollected convicted offender DNA profiles are "owed"
to the system.
An equally important but more difficult problem to quantify is that of
unprocessed casework that contains biological evidence. This casework
backlog may include nonsuspect or unsolved cases that could be analyzed
solved as a result of advancements in DNA technology.
Convicted offender backlogs
Although all 50 States have passed DNA database legislation, many States
have backlogs of convicted offender samples that have been collected but
not yet been analyzed. Although Federal funding has played an important
reducing existing backlogs, the crimefighting potential of DNA has prompted
many States to revise their statutes to require nonviolent convicted offenders
provide a DNA sample for analysis and upload into CODIS. The trend toward
expanding convicted offender DNA statutes to include nonviolent offenders
significantly increased the number of DNA samples requiring collection
analysis. Although the success of using the DNA database as a crime-solving
and crime-prevention tool can easily be demonstrated once convicted offender
backlogs are reduced, it should be recognized that new backlogs are instantly
created by the passage of expanded DNA legislation laws. Convicted offender
backlogs are an ongoing logistical issue that can compound the complexity
investigating cold cases by using the DNA database.
Forensic casework backlogs
Addressing issues that affect the efficient and effective use of DNA databases
the United States is complicated further by the existence of casework
This refers to biological evidence in perhaps tens of thousands of criminal
including violent and nonviolent crimes, that has not been tested or retested
Unprocessed rape kits are a clear example of this kind of backlog. Despite
established fact that rape typically yields biological evidence, as of
1999, at least 180,000 rape kits remained on shelves across the country,
unprocessed, because no suspects have been identified. The DNA evidence
from these and other criminal cases often is not analyzed and entered
DNA database because forensic laboratories have to prioritize their work
cases scheduled for trial take precedence over cases in which no suspect
known. In most jurisdictions, nonsuspect criminal cases that contain biological
evidence are not being analyzed and entered into the DNA database. In
jurisdictions, DNA from crime scenes is still primarily used to prosecute
offenders, not to investigate crimes. The convicted offender backlog and
resources for casework going to trial preclude State forensic laboratories
analyzing all biological evidence for DNA, which in turn prevents law
enforcement from being able to realize the full crime-solving potential
The backlog of forensic cases has practical consequences for most law
enforcement agencies in the United States. Laboratory capacity limitations
result in the ability to process crime scene samples from only the most
of offenses. More and more, however, agencies such as those in the United
Kingdom are discovering the value of DNA technology in solving property
crimes. Blood left on a broken apartment window or saliva found on a
discarded beer bottle can be used to identify burglars, and the skin cells
off onto the steering wheel of a stolen vehicle can solve car thefts.
long as forensic laboratories remain able to process only the most serious
cases, the full potential of DNA technology to solve crime will remain
A broad range of considerations must be made long before any DNA testing
actually attempted in older, unsolved cases. These include--
Legal considerations, such as the application or expiration of statutes
Technological considerations, such as the nature and condition of the
evidence as originally collected, stored, and in some instances, subjected
other forensic tests.
Practical considerations, such as the availability of witnesses in the
DNA testing would identify a suspect and lead to an arrest and a trial.
o Resource issues, such as the time and money available for investigation
The nature and scope of these issues require that any approach to reexamining
old cases for potential DNA evidence be collaborative, whether by an
individual investigator or by a specialized unit developed specifically
case review. Local prosecutors can provide valuable insight into legal
that might prevent or help a future prosecution. Victim/witness units
advocates can provide valuable assistance with locating, educating, and
encouraging witnesses. Consultation with representatives from the crime
laboratory is critical to ensuring that potential DNA evidence can be
When collecting unsolved case evidence from storage facilities, the case
investigator should be ready to handle all types of packaging disasters.
Evidence may be stored in heavy-duty plastic bags, stapled shut as the
form of "sealing." Multiple items may be sealed in one plastic
bag, or even
unpackaged in large, open, cardboard boxes. Unprotected microscope slides
from medical facilities might also be found as a result of investigating
No attempt should be made on the part of the investigator to separate
repackage evidence. The condition and position that the evidence has been
stored in could provide valuable clues to the forensic scientist for testability
evidence. Only when evidence is found unpackaged should the investigator
properly package and label the item(s) to minimize the possibility for
contamination from that point forward. It is important that any evidence
are handled minimally and only by individuals wearing disposable gloves.
always, it is also very important that all actions taken as a result of
evaluating, packaging, or repackaging evidence are documented thoroughly
the case folder.
Prior to the frequent use of DNA technology, biological evidence may have
been collected and stored in ways that were not necessarily the best methods
for preserving samples for future DNA testing. For example, evidence
containing biological fluids that were originally collected for ABO Blood
analysis or other serology methods may have been packaged or stored in
that can limit DNA testing. Some methods of collection and storage may
promote the growth of bacteria and mold on the evidence. Bacteria can
seriously damage or degrade DNA contained in biological material and inhibit
the ability to develop a DNA profile; however, evidence can still sometimes
yield DNA results. For example, PCR technology can allow the laboratory
develop profiles from some moldy biological samples, whereas other evidence
may fail to yield a usable DNA profile, even when no mold is visible.
close consultation with the laboratory is important to determine the type
DNA testing most likely to yield results on the available evidence.
Because of the particularly sensitive nature of DNA technology, the potential
contamination of evidence should be carefully considered. Technologies
analyze evidence prior to the forensic application of DNA were not always
sensitive to contaminants. Evidence in older cases may have been collected
ways that lacked appropriate contamination or cross-contamination safeguards,
which can make the DNA results less useful or even misleading. In these
clarifying results by identifying the contributor of an additional profile
determine whether the DNA results may now be used. When a mixture is
detected, a careful reconstruction of the evidence collection, storage,
analysis process must be undertaken. It may be determined that DNA profiles
will be required from on-scene officers, evidence technicians, or laboratory
scientists who had access to the evidence for comparison with evidence
In these instances, proper chain-of-custody reconstruction is critical.
It is also important to avoid contamination when handling biological evidence
during the course of the current review. If evidence that may contain
material is already sealed, do not reopen it before sending it to the
(See Evidence Handling Recommendations.)
Numerous legal issues might arise when examining older cases for potential
DNA evidence. These issues are most likely jurisdictionally specific and
differ from State to State. Although most jurisdictions maintain no statute
limitation for filing charges in a homicide case, States can vary widely
in the time
allowed for filing charges in other cases, such as rape and other sexual
crimes. Furthermore, in recognition of DNA technology's ability to solve
cases, many States are extending or even eliminating statutes of limitation
Chain of custody
When a case remains unsolved for a long period of time, evidence is usually
handled by an increased number of individuals. Many unsolved cases to
reviewed for DNA evidence may have been previously reinvestigated or
handled by several different investigators as a result of new leads or
systematic reviews. Furthermore, as cases age, the likelihood increases
evidence may be moved to new or remote storage locations as evidence from
newer cases fills police department shelves.
Many cases may also have had evidence submitted to the laboratory for
forms of forensic testing. Evidence in older cases may have been submitted
standard serological testing, but can now be tested for DNA with much
success. Hair previously submitted for standard microscopic hair analysis
now be submitted for mtDNA testing. As with all criminal investigations,
chain-of-custody issues are critical to maintaining the integrity of the
In all cases, the ultimate ability to use DNA evidence will depend on
to prove that the chain of custody was maintained.
Statutes of limitation
One of the first issues to address when reviewing an unsolved case is
the statutes of limitation on a case have run out. Several considerations
when addressing a statute of limitation issue. Good communication between
enforcement and local prosecutors is critical when examining these legal
Changes in statutes. Advances in DNA technology and the creation of DNA
databases are leading many criminal justice professionals to rethink time
placed on the filing of criminal charges. Because biological evidence
reliable DNA analysis results years after the commission of a crime, many
legislatures have begun to extend, and in some cases eliminate, the statutes
limitation for some crimes and in certain circumstances. Many States have
extended the length of time for which a complaint can be filed, other
have eliminated statutes of limitation for certain crimes, and some legislation
Exceptions to statutes. Exceptions often exist under existing and new
Under such exceptions, time can be added to the statute of limitation,
police the legal authority to arrest even if it appears as though the
statute has run
out. For example, many jurisdictions have exceptions for a suspect's flight
jurisdiction. In a case for which there is a 5-year statute of limitation,
government can prove that the suspect has been absent from the jurisdiction
2 years, the State can still file against the suspect for up to 7 years
commission of the crime. Exceptions also exist for cases in which child
are assaulted by a family member, which can be valuable in the context
Victim and witness considerations
Another important consideration to be made early in the process is the
willingness of victims and witnesses to proceed. Although many victims
continuously monitor the progress of their investigations, some choose
from the process over time. Reinvestigating a case may cause renewed
psychological trauma to the victim and victim's family. It should not
that victims and witnesses, even if they were eager to pursue the case
occurred, are still interested in pursuing the case. A phone call from
investigator years later may not be a welcome event. Whenever possible,
the aid of victim service providers. If a new officer is handling the
enlisting the assistance of the original investigator to make the first
the victim may also be helpful.
The older a case is, the more difficult it may be to locate witnesses.
early identification of victim and witness availability may ultimately
significant resources. Consultation with prosecutors is mandatory when
considering whether a witness would be necessary at trial.
Identifying, Analyzing, and Prioritizing Cases
Whether the process of reviewing unsolved cases is initiated by a single
or by a specialized unit, it must ultimately be a team effort. At all
stages of the
process, investigators should avail themselves of the scientific advice
laboratory and the legal expertise of the local prosecutor's office. Close
consultation with the laboratory can ensure that evidence integrity is
and that limited laboratory resources are allocated effectively. Similarly,
prosecutors can help identify issues that might occur at trial if a suspect
identified and arrested upon successful DNA testing. Good communication
between police, laboratories, and prosecutors can help identify and convict
serious offenders and save valuable time and resources.
Identify potential cases for review
An initial step in the DNA review of unsolved cases is to identify cases
might be amenable to DNA testing. While the cases considered for this
review will vary from jurisdiction to jurisdiction, it is important to
minimum requirements that will likely benefit from this approach. Issues
statutes of limitation and solvability factors should be thoroughly examined
cooperation with a prosecutor and the forensic laboratory to establish
guidelines for case selection. It also will be important to identify the
goals of the program so that the selection criteria can be tailored to
Cases that could benefit from a review for potential DNA evidence can
identified from numerous sources. In some instances a single police officer
investigator may remember an unsolved case from years ago. In some
departments a formalized cold-case unit may systematically review cases
potential of DNA testing. Other cases may be identified by coordinated,
interdepartmental efforts, victims or witnesses who have heard about the
potential of DNA evidence, and laboratories taking inventory of their
facilities. If a department is pursuing a systematic review of cases,
either by one
or two officers or by a formal unit, there are many sources that can be
consulted for valuable investigative information, such as--
o Autopsy, laboratory, prosecutor, and local agency logbooks.
o Retired investigators.
o Computer databases
Identify statute of limitation issues
Statute of limitation issues might affect the ultimate ability to prosecute
Cases should be preliminarily reviewed by investigators in conjunction
prosecutor's office to identify which prosecutions would be barred by
statutes of limitation. If the goal of the unsolved case review program
obtain convictions and statutes of limitation have expired on a particular
department may wish to save its resources for cases likely to yield convictions.
However, if the goal of the program is to solve and close unsolved cases
regardless of whether a conviction could be obtained, a jurisdiction may
to review all cases that qualify under its guidelines. This is an important
consideration in the context of investigating serial offenders whose criminal
might span the course of years or decades.
Define categories of cases--solvability factors
Because the number of cases that qualify for reinvestigation might be
it may be beneficial for a jurisdiction to define cases according to several
solvability factors. Solvability factors include facts and circumstances
of a case
that influence the likelihood that it might be solved through advancements
DNA technology. For example, a high probability exists that analysis of
nonsuspect rape kits will yield valuable DNA results. Profiles generated
result of DNA analysis can now be entered into CODIS, which can solve
case by matching to a convicted offender, or aid investigations by linking
rapes to each other. Additionally, if an unsolved murder case contains
evidence foreign to the victim that did not produce viable results from
blood typing or RFLP DNA analysis, evidence could be reanalyzed with the
more discriminating and powerful STR technology. It is also important
recognize and sort out cases that might not be as likely to be solved
technology. An example might be an unsolved drive-by homicide because
perpetrator most likely would not have left biological evidence at this
Case review--establish priorities
Once solvability factors and statute of limitation issues are addressed,
important to continue the process by identifying the cases to be reviewed
To preserve investigative resources when considering a larger number of
unsolved cases for review, jurisdictions may prioritize according to the
likelihood that cases will be solved or the likelihood that investigations
aided. In establishing this priority, the following criteria can be considered:
o How many qualifying cases are there?
o Where are the case files located?
o Are case summaries available?
o How many cases will be assigned to an investigator?
To establish an investigative hierarchy, qualifying cases should be reviewed
experienced, proficient investigators. A checklist can be used throughout
review process so that managers can decide which cases will be worked
A checklist can also provide review process consistency throughout the
(See Sample Checklist at the end of this report.) The following categories
serve as a model for a hierarchy in prioritizing cases:
o There is a known suspect and physical evidence appears to have been
preserved in a manner consistent with successful DNA testing and use of
o There is no known suspect but physical evidence has been preserved in
manner consistent with successful DNA testing and use of CODIS.
o There is no known suspect and evidence was collected and preserved in
manner that may make it difficult to obtain a DNA profile.
Locating case files, obtaining evidence logs, and other documentation
Locating the case file and original evidence for the investigation may
challenging endeavor. Changes in personnel, procedure, and facilities
passage of time may complicate the process. When searching for a case
evidence, an investigator may need to look in numerous places. Potential
locations include, but are not limited to, the following:
o Police department property rooms (case files, evidence logs, whole
o Property warehouses (case files, evidence logs, whole evidence).
o Public crime laboratories (previously tested/submitted evidence, lab
o Private laboratories (previously tested evidence, lab reports).
o Hospital/medical facilities (rape kits, medical reports, slides).
o Coroner/medical examiners' offices (autopsy reports).
o Courthouse property rooms.
o Prosecutors' offices (previous trial or suspect investigation).
o Retired investigators' files (case notes and details not contained in
o Other investigating agency offices (investigative leads--serial offender).
Forensic testing reports and previously tested evidence
Because advancements in DNA technology enable laboratories to successfully
analyze old evidence that might have been improperly stored or subjected
previous forensic analysis, it will be very valuable to locate any and
reports that were produced as a result of previous analysis and/or testing.
blood typing, microscopic hair analysis, RFLP DNA analysis, or fingerprint
analysis (among others) might have been performed in the course of the
investigation. The original case file should indicate whether and which
forensic analysis were attempted. These reports also serve to memorialize
proper chain of custody. Cooperation with the crime laboratory is crucial
locate and interpret existing forensic reports and to determine whether
would be amenable to reanalysis with new DNA techniques.
Many combinations of options are available to investigators and laboratory
personnel if biological evidence was available and previously tested.
may serve to help investigators as they work with the laboratory to discuss
options throughout the course of the investigation.
Locate biological evidence
When reviewing the case file for potential DNA evidence, it is important
know what kinds of evidence may yield a DNA profile. Given the power and
sensitivity of newer DNA testing techniques, DNA can be collected from
virtually anywhere. Only a few cells can be sufficient to obtain useful
information to help solve a case. Exhibit 4 identifies some common items
evidence that may have been collected previously but not analyzed for
presence of DNA evidence. Remember, if a stain is not visible it does
that there are not enough cells for DNA typing. Further, DNA does more
just identify the source of the sample; it can place a known individual
at a crime
scene, in a home, or in a room where the suspect claimed not to have been.
can refute a claim of self-defense and put a weapon in the suspect's hand.
also provide irrefutable evidence that can change a suspect's story from
to one of consent.
Evaluate for probative DNA evidence
On completion of reviewing the case file, reports, and evidence in consultation
with the laboratory, it will be necessary to identify which evidentiary
be amenable to DNA analysis. Consultation with the laboratory will be
to determine the likelihood of obtaining results from DNA analysis, and
consultation with a prosecutor is very important to determine which evidence
will be probative to the case. Building the new investigation on cooperative
efforts between the laboratory and prosecutor can save valuable resources,
develop leads, and identify previously overlooked evidence that may yield
Continue investigative protocol
If DNA analysis is to be conducted, it may be important to obtain reference
samples from prior suspects, and it might be necessary to be creative
obtaining these samples. While a biological sample in the form of blood
saliva can be obtained voluntarily through a consent form, a standard
sample might already exist if previous forensic analysis, such as serological
testing, was performed during the course of the original investigation.
Additionally, elimination samples from anyone who had lawful access to
crime scene, such as family members, may be required if the laboratory
determines that there is more than one DNA profile present in the evidence
sample. Early identification of the location and status of persons who
requested to submit an elimination sample could save valuable time and
resources if the laboratory needs such information. Consultation with
laboratory is essential to properly coordinating this process.
Follow agency procedures for submitting the DNA profile to CODIS
On successful laboratory analysis resulting in a DNA profile developed
crime scene evidence, existing and/or new suspect DNA profiles should
compared with the evidence profile. If the laboratory determines a match
between a suspect and the evidence, the prosecutor's office should be
consulted on how to proceed. However, if a match is not found, agency
procedures should be followed, in accordance with the crime laboratory,
submit the crime scene evidence DNA profile into CODIS.
Because CODIS contains hundreds of thousands of convicted offender DNA
profiles, it is possible that the person who committed the unsolved crime
investigated was convicted of a qualifying offense that required submission
DNA profile to the database. If that person has not previously been convicted
of a qualifying offense, especially in light of expanding database law,
possible that they will be convicted in the future. Further, because the
index of CODIS contains thousands of crime scene evidence profiles, the
investigation could be aided if a match is made to another forensic DNA
already in the database. Finally, an investigator should not assume that
DNA profile generated from unsolved case evidence and submitted to the
laboratory for entry into CODIS will be compared with every possible
convicted offender or crime scene index profile. The investigator may
proactively request that his CODIS administrator search the new profile
the local, State, and national DNA databases.
Prepare a John Doe warrant
CODIS is a powerful crime-solving and crime-prevention tool, but many
will not be solved as a result of entering a DNA profile into the forensic
the database. Additionally, many cases will have statute of limitation
might prevent the prosecution of the case if a match is not determined
timely manner. Therefore, if no offender match occurs in cases in which
of limitation are an issue, consideration may be given, in consultation
prosecutor, to preparing a John Doe warrant. These types of warrants can
identify the perpetrator according to his or her DNA profile. The 13-loci
generated by the crime laboratory should be clearly printed on the face
warrant. The John Doe warrant is not novel; however, the unconventional
method of describing an individual by his or her DNA profile may allow
prosecution of a case if a DNA match is determined in the course of future
investigations or as a result of the CODIS system being populated with
convicted offender and forensic DNA profiles.
1. CODIS uses two indexes--the forensic index and the offender index--to
generate investigative leads in crimes where biological evidence is recovered
from crime scenes. The forensic index contains DNA profiles of biological
crime scene evidence and the offender index contains DNA profiles of
individuals convicted of a qualifying offense.
2. CODIS has a missing persons index that exclusively contains mtDNA
profiles; the convicted offender and forensic indexes of CODIS exclusively
contain STR DNA profiles.
The successful review and investigation of unsolved cases require cooperation
among law enforcement, the crime laboratory, and the prosecutor's office.
The power of a DNA database system is evident not only in the success
solving crimes previously thought unsolvable, but through the prevention
The reliability of DNA technology may necessitate the reevaluation of
If biological evidence is available for testing or retesting in unsolved
investigations, it is important that law enforcement and the crime laboratory
work together to review evidence.
If the convicted offender or forensic index of CODIS is to be used in
investigative stages of an unsolved case, DNA profiles must be generated
A "forensic hit" occurred in the National DNA Index System (NDIS)
linked a dead Florida man's DNA profile to eight serial unsolved rapes
Washington, D.C. and three offenses in Florida.
In 1999, Leon Dundas was killed in a drug deal. Investigators remembered
Dundas refusing to give a blood sample in connection with a rape investigation
in 1998. They were able to obtain Dundas' blood sample through the medical
examiner's office and forwarded it to the DNA lab at the Florida Department
Law Enforcement. Dundas' DNA profile was compared with the national
forensic index and a match was made between Dundas and DNA evidence
from a rape victim in Washington, D.C.
The FBI then entered DNA evidence from additional unsolved rapes
committed in Washington. Dundas' DNA matched seven additional rapes in
Washington and three more in Jacksonville, Florida. Police in Washington
that without DNA, they would have never identified Dundas, who had no
recorded history of violent crime.
The offender index contains DNA profiles of individuals convicted of certain
crimes. The forensic index contains DNA profiles obtained from crime scene
Local prosecutors can provide valuable insight into legal issues. Victim/witness
units or advocates can help locate, educate, and encourage witnesses.
Consultation with representatives from the crime laboratory is critical.
Evidence Handling Recommendations
o Wear gloves. Change them between handling each item of evidence.
o Use disposable instruments or clean instruments thoroughly before and
handling each evidence sample.
o Avoid touching the area where you believe DNA may exist.
o Avoid touching your face, nose, and mouth when examining and repackaging
o Put dry evidence into new paper bags or envelopes; do not use plastic
o Do not use staples.
o If repackaging of evidence is necessary, consult with laboratory personnel.
Statute of Limitation Recommendations
o Know the original statute of limitation.
o Determine whether the law has changed regarding time limits for filing.
If so, is
the law retroactive?
o Determine whether there are exceptions to the statute.
o Consult with the prosecutor.
It should not be assumed that victims and witnesses are still interested
pursuing the case. Whenever possible, enlist the aid of victim service
Good communication between police, laboratories, and prosecutors can help
identify and convict serious offenders and save valuable time and resources.
DNA Can Do More . . . . . . than identify a suspect. It can also--
o Place a known individual at a crime scene.
o Refute a claim of self-defense.
o Put a weapon in a suspect's hand.
o Change a suspect's story from an alibi to one of consent.
o Identify potential cases.
--Identify any statute of limitation issues (consult with prosecutors).
--Define case categories according to solvability factors.
o Prioritize cases (consider solvability factors).
o Locate and review the case file; obtain evidence logs and other
documentation such as laboratory and autopsy reports.
o Locate previous forensic testing reports and location of previously
--Blood previously ABO typed.
--Hair analyzed microscopically.
o Locate crime scene evidence containing biological material.
o Evaluate the case and evidence for potential probative DNA. Be sure
--Consider all evidentiary possibilities.
--Take appropriate precautions against contamination.
o In consultation with the laboratory and prosecutors, submit appropriate
(probative) evidence to the laboratory for testing.
o Continue investigative protocol. If needed, obtain reference samples
--Voluntarily using a consent form.
--By using a previously obtained sample (e.g., if a reference sample was
for standard serological testing).
o Identify witness issues--
--Willingness to proceed.
o If a profile does not match suspect profiles, follow agency procedures
submitting the evidence profile to CODIS.
o If no offender match occurs in cases in which statutes of limitation
issue, prepare a John Doe warrant.