In crimes of violence, bloodstained evidence, if properly handled, is very valuable. Sometimes the evidence is in the form of fresh or clotted blood. More often, it is in the form of fresh or dried bloodstains. Blood clots and bloodstains require careful examination. No blood clot or bloodstain is so characteristic in appearance that you can definitely tell its origin.
The body has a defense mechanism against excessive bleeding. As soon as bleeding starts in any great quantity, the blood pressure automatically drops. Consequently, the rate of bleeding slows. Upon death, blood pressure falls to zero and bleeding ceases. The only exception is a large wound located where drainage due to gravity will occur. This drainage is a mixture of blood cells, serum, and often, other materials. It is generally quite dark in color, and may collect in great quantity. The amount of blood around a body may be important. A lot of blood seemingly coming from a small wound would indicate that the victim survived the attack for a fair length of time.
Blood, as it dries, darkens in color until, when completely dried, it turns reddish-brown or dark brown. An old, dried blood clot may become so dark that it is almost black. Blood may fall on porous material, like cotton, wool, blotting paper, porous brick, or soft wood. Should this happen, the original color may be changed by its being absorbed into the porous material. And mold, putrefaction, or chemical changes may cause bloodstains to appear to be black, green, or blue to grayish-white instead of the usual reddish-brown. The color of the blood should be noted.
A bloodstain on a dark background may be hard to see. A flashlight may help you see the bloodstain. Under artificial light, a dried bloodstain on a dull background may appear as a glossy or flat varnish. Indoors, with limited light, dried bloodstains on a dark surface may be made more visible by shining a flashlight beam parallel to the floor.
SHAPE, PERSISTENCY, AND AGE
The shape of bloodstains may yield important information about the circumstances of a crime. In many cases the height from which a drop of blood fell may be told by the appearance of the bloodstain. The hydrodynamics of bloodstains and splashes help in the reconstruction of crimes. The surface on which blood falls influences its shape, as does the height from which it drops. On a smooth surface, if the height of the fall is short (6 to 12 inches), the bloodstains may appear as circular disks. If the height is from 12 to 60 inches, the edges of the bloodstain may be jagged. This jaggedness increases as the height increases. The greater the height, the more jagged the edges. If a drop falls from an even greater height (2 or 3 yards), it may splash on impact and form many small bloodstains. These are often concentrated around a large central bloodstain, giving a sunburst appearance.
Drops of blood which strike a surface at an angle may bounce or splash. This leaves a large, main, teardrop-shaped blot with a series of smaller blots trailing off in the direction of fall. The pattern is similar in appearance to an exclamation point. Often the larger splash is made first and the smaller ones afterwards.
Do not make hasty conclusions about the direction of travel of a person from the appearance of bloodstains. The material on which blood falls may change the original shape of a drop as it strikes. Bodily movement can cause blood to fall in a direction opposite to that in which the person is traveling. The shape of a bloodstain also depends on the blood's viscosity at the time it drops and the composition of the material it hits.
Sometimes, blood may be identified on skin or a garment that has been washed, if the washing is not thorough. If a garment has been washed with soap and water, residual bloodstain traces often cannot be identified as blood. But washing of the hands may fail to remove all traces of blood. Look for blood traces under fingernails and around cuticles.
There is no way to judge the age of a bloodstain with any degree of certainty. Clotting time can be altered by many factors. Blood usually clots in 10 to 20 minutes. Examination of the clot may help you determine how much time has elapsed since the stain was made. Clotting is more rapid on a rough surface than on a smooth one. Oily substances may increase the clotting time. They can also alter the appearance of the blood. Even the peculiarities of someone's blood may affect the clotting time. A single drop of blood that falls on a dry surface often dries in about an hour at room temperature. Blood that has collected in a pool dries slowly. The drying time depends on the size and depth of the pool. Temperature and humidity also affect the drying time.
Microscopic examination may disclose the origin of the blood. Mucus or hairs from the nostrils may be found in blood from the nose. Semen and genital hairs may be found in blood from a rape. Certain cells from the vagina may be in blood from menstruation. However, the absence of these elements or particles does not necessarily disprove that the blood originated in the part of the body from which it was believed to have come.
The value of the information gained through the examination of bloodstain evidence depends mainly on your use of proper methods in collecting, identifying, preserving, and shipping the evidence to the crime lab.
Damp articles to be checked for trace evidence should not be packed or sent to the crime lab until they have thoroughly dried. Garments from the victim and suspect should not be dried in the same room. A covering for the garments can be used to reduce any disturbance. Bloodstains must be allowed to dry naturally. Heat or fans should not be used. If heat is applied to a bloodstain, physical changes take place within the bloodstain. A fan may blow foreign material onto the bloodstain. And the airstream from a fan may remove hairs, fibers, or other microscopic particles that may have a bearing on the case.
Use clean wrapping paper to pack bloodstained articles. Wrap each bloodstained article separately before it is boxed for shipment to the lab. Wrapping prevents stains or other microscopic evidence from being transferred from one article to another.
When a bloodstain is on clothing, the entire garment, whenever possible, should be sent to the lab to ensure a complete analysis. When a bloodstain is on a large object, such as a rug or a drape, the bloodstained portion may have to be removed. Included some of the unstained material from near the bloodstain for use as a control sample. In all cases, send as much of the dried stain as possible. A photo of the item detailing the stained area should accompany the sample.
When the bloodstains are on fixed objects or objects too bulky to be sent easily, other means should be used. The part of the object bearing the stain should be removed and sent to the lab, if at all possible. Stains may be on objects which cannot be cut, such as concrete floors or metal safes. Objects such as these are scraped and the crusty portion of the stain placed on a clean piece of paper. The paper is then folded and placed in a proper container. The remainder of the stain is taken up on a swab dampened with distilled water. Rub the swab on the stain, let the swab dry, and place it in a container. For control testing, an unstained area near the bloodstain should be swabbed, dried, placed in another container, and sent to the lab.
If the bloodstain is on a porous material like wood or earth, send the bloodstain and a portion of the material the bloodstain is on. Thus, proper control tests can be made. Place the material in a clean pillbox or similar container. Then label the container with identifying data and seal it to prevent leakage.
Sometimes, you must get liquid blood samples to send to the lab with other evidence. Blood samples should be drawn by a medical officer or a trained medical technician. Medical personnel may take samples of body fluids like blood and urine from soldiers without their consent when authorized to do so by a search warrant or search authorization. Fluid samples may be taken from nonconsenting soldiers without a warrant or authorization if there is clear evidence that a delay could destroy the evidence. The samples should be taken at a medical facility where proper precautions can be taken to prevent contamination of the samples. Medical facilities have sterile containers available for sending samples to the lab.
The amount of liquid blood needed for lab examination is about 5 cubic centimeters or one-sixth of an ounce. Two tubes of blood should be sent: one with an anticoagulant, the other without. Do not add any preservatives to whole blood. They interfere with the blood tests. If there is a delay in sending drawn blood to the lab, use refrigeration. But the sample must not be frozen.
Send blood samples to the lab by the fastest means to keep them from deteriorating. The quickest means is usually registered mail or a courier traveling by air. Do not package a liquid blood sample with other specimens. If the container breaks or leaks, it could contaminate other evidence in the package. Liquid samples should be shipped in properly labeled, sterile, tightly sealed glass containers. They must be packed to prevent breakage.
Preliminary lab examinations of an alleged bloodstain use chemical tests to tell if the stain is a bloodstain. If the results are negative, the stain cannot be blood. If the results are positive, further examination and testing are required. The chemical tests may not be conclusive. Other substances, common chemical compounds, and certain body discharges may also give positive results. The lab's inability to provide information on bloodstain evidence is often due to unsuitable samples. Unsuitable samples are caused by late shipment or contamination of the evidence.
If testing shows that the stain is a bloodstain, it must be learned if the blood is human. The evidence value of a bloodstain may be seriously impaired unless the stain is shown conclusively to be human blood. A suspect may claim that the stain is blood from an animal that the suspect has handled in some way.
The preferred test for human blood is the precipitin test. The test is a complicated lab process. It requires an adequate blood sample. For this reason, you should send as much of a bloodstain as you can to the lab. The minimum amount needed for this test cannot be stated because reactions vary according to the condition of the sample. The lab approach to the problem will depend on the size and condition of the bloodstain. The nature of the object bearing the bloodstain also affects the test.
If the blood is determined to be human, it can be tested to determine its blood grouping. The blood of every human being belongs to one of four blood groups: O, A, B, or AB. Blood grouping is based on the presence or absence in the blood of group-specific substances, either singly or in combination. The blood group is not changed by time or disease.
Grouping dried bloodstains is more difficult than grouping liquid blood. The age of the bloodstain or the degree of exposure to direct sunlight, extreme temperatures, and other natural conditions may yield changes that reduce the possibility of successful grouping. In the case of a putrefied or embalmed corpse, grouping tests may be done on the tissues.
For blood group testing, the lab needs more than a small spot
of blood. If specimen quantity is limited, the grouping tests
may have to be eliminated entirely. Testing is then limited to
chemical and, precipitin tests. Larger samples improve the chance
of getting the most information from lab tests. A fairly heavy
bloodstain measuring 1/2 inch by 1/4 inch is usually enough for
a conclusive grouping test. Samples less than this size must not
be arbitrarily discarded as being insufficient. Testing may also
show blood group subgroupings, Rhesus factor, MN grouping, polymorphic
proteins, and the presence of some diseases.