Reference Citation: An earlier version of this paper was published as Schiro G. Collection and Preservation of Evidence. In: Muth AS, editor. Forensic Medicine Sourcebook. Detroit: Omnigraphics, 1999; 45-59.
George Schiro, MS, F-ABC
COLLECTION AND PRESERVATION OF EVIDENCE
Once the crime scene has been thoroughly documented and the locations of the evidence noted, then the collection process can begin. The collection process will usually start with the collection of the most fragile, most easily contaminated, or most easily lost evidence. Special consideration can also be given to any evidence or objects that need to be moved. Collection can then continue along the crime scene trail or in some other logical manner. Photographs should also continue to be taken if the investigator is revealing layers of evidence that were not previously documented because they were hidden from sight.
Most items of evidence will be collected in paper containers such as packets, envelopes, and bags. Liquid items can be transported in non-breakable, leak-proof containers. Arson evidence is usually collected in air-tight, clean metal cans. Only large quantities of dry powder should be collected and stored in plastic bags. Moist or wet evidence (blood, plants, etc.) from a crime scene can be collected in plastic containers at the scene and transported back to an evidence receiving area if the storage time in plastic is two hours or less and this is done to prevent contamination of other evidence or other surfaces. Once in a secure location, wet evidence, whether packaged in plastic or paper, must be removed and allowed to completely air-dry. That evidence can then be repackaged in a new, dry paper container. UNDER NO CIRCUMSTANCES SHOULD EVIDENCE CONTAINING MOISTURE BE SEALED IN PLASTIC OR PAPER CONTAINERS FOR MORE THAN TWO HOURS. Moisture allows the growth of microorganisms that can destroy or alter evidence.
Any items that could cross contaminate each other must be packaged separately. The containers should be closed and secured to prevent the mixture of evidence during transportation. Each container should have: the collecting person's name or initials; the date and time it was collected; a complete description of the evidence and where it was found; and the investigating agency's name and their file number.
Each type of evidence has a specific value in an investigation. The investigator must determine the type of evidence that is going to provide the most useful information and spend more time collecting that type of evidence than the other types of evidence. For example, in some cases, such as homicides, fingerprints and DNA evidence might have more value than fibers left by a suspect's clothing. In other cases, such as hit and run cases, trace evidence might have more value than fingerprint evidence. Trace evidence can also provide valuable investigative information that other types of evidence cannot. It is also wise to collect more evidence at a crime scene than not to collect enough evidence. An investigator usually only has one shot at a crime scene, so the most should be made of it.
The following is a breakdown of the types of evidence encountered and how the evidence should be handled:
FINGERPRINTS (also includes palm prints and bare footprints) - the best evidence to identify an individual's presence at the scene of a crime. Collecting fingerprints at a crime scene requires very few materials, making it ideal from a cost standpoint. All non-movable items at a crime scene should be processed at the scene using gray powder, black powder, or black magnetic powder. Polaroid 665 black and white film loaded in a Polaroid CU-5 camera with detachable flash or another suitable camera should be used to make natural size photographs of prints that do not readily lift. Contact DNA is DNA left by a person coming in contact with an item, such as a knife handle, gun, steering wheel, doorknob, etc. Heavy smudges should be lifted for potential contact DNA. When processing a scene with the potential of contact DNA, fresh, uncontaminated powder should be used and brushes should be sterilized with UV light between scenes to prevent cross contamination. All small transportable items can be packaged in paper bags or envelopes and sent to the crime lab for processing; however, depending on the nature of the items, they might be best processed at the scene as well. Because of the "package it up and send it to the lab" mentality, some investigators skim over collecting prints at a crime scene. Collecting prints at the crime scene should be every investigator's top priority. Fingerprints from the suspect as well as elimination fingerprints from the victim will also be needed for comparison (the same holds true for palm and bare footprints).
BLOOD, BODY FLUIDS, AND CONTACT DNA EVIDENCE- DNA evidence can be associated directly to an individual or it can be associated to an individual with a high degree of probability. Dried blood, body fluid stains, and items with potential contact DNA should be collected in the following manner: If the item can be transported back to the crime lab, then package it in a paper bag or envelope and send it to the lab. If the object cannot be transported, then use sterile swabs moistened with sterile, deionized, or distilled water or other suitable solvent such as 70% ethanol (first check with your crime lab to make sure this is OK) and swab the stain or source of possible contact DNA. Allow the swabs to air-dry and then package them in separate paper envelopes. Wet blood and body fluid stains should be collected in the following manner: All items should be packaged separately to prevent cross contamination. If the item can be transported to the crime lab, then package it in a paper bag (or plastic bag if the transportation time is under two hours), bring it to a secure place and allow it to thoroughly air-dry, then repackage it in a paper bag. If the item cannot be transported back to the lab, then absorb the stain onto at least two sterile cotton swabs. Allow the swabs to air-dry and then package them in paper envelopes. If it cannot be dried at the scene, package it in paper (or plastic if the transportation time is less than two hours), bring it to a secure place and allow it to thoroughly air-dry, then repackage it in a paper envelope. UNDER NO CIRCUMSTANCES SHOULD WET OR MOIST ITEMS REMAIN SEALED IN PLASTIC OR PAPER CONTAINERS FOR MORE THAN TWO HOURS. Victim and suspect's reference DNA samples, usually either a buccal swab (a swab of the cheek walls inside the mouth) or a whole blood samples collected in a purple top "Vacutainer" must be obtained and submitted to the lab. Contact the lab to which the samples will be submitted for specific information.
BITE MARKS - usually found associated with sexual assaults or fights. They should be photographed using an ABFO No. 2 Scale with normal lighting conditions, side lighting, UV light, infrared light, and alternate light sources. Digital, color slide, print film, black and white film, and infrared film should be used. The more photographs under a variety of conditions, the better. The bitemark can even be documented with video. The bitemark should also be swabbed for potential DNA evidence. A bitemark that has left an impression can be cast. Older bitemarks which are no longer visible on the skin may sometimes be visualized and photographed using UV light and alternate light sources. Casts and photographs of the suspect's teeth and maybe the victim's teeth will be needed for comparison. For more information consult a forensic odontologist.
BROKEN FINGERNAILS- A broken fingernail found at a crime scene can be matched to the individual from which it came many months or years after the crime has been committed through microscopic or DNA analysis. Broken fingernails should be placed in a paper packet, which is then placed in a paper envelope. It can then be transported to the crime lab for analysis. Known fingernail or DNA samples from the suspect and maybe from the victim will be needed for comparison.
QUESTIONED DOCUMENTS- handwriting samples can also be examined for characteristics in common to an individual's handwriting. Known exemplars of the suspected person's handwriting must be submitted for comparison to the unknown samples. Questioned documents can also be processed for fingerprints, contact DNA, and indented writing. All items should be collected in paper containers. For more information consult a questioned documents examiner.
FIREARMS AND TOOLMARKS - bullets and cartridge cases found at the crime scene can be matched back to a gun in the possession of a suspect. Bullets and cartridge cases can also be examined at the crime lab and sometimes tell an investigator what makes and models of weapons may have expended the case or bullet. Toolmarks can be matched to a tool in the suspect's possession.
Firearm safety is a must at any crime scene. If a firearm must be moved at a crime scene, never move it by placing a pencil in the barrel or inside the trigger guard. Not only is this unsafe, but it could damage potential evidence. Using gloves, the gun can be picked up by the textured surface on the grips without fear of placing unnecessary fingerprints or DNA on the weapon. Before picking up the gun, make sure that the gun barrel is not pointing at anyone. Keep notes on the condition of the weapon as found and the steps taken to render it as safe as possible without damaging potential evidence. The firearm can then be processed for prints or contact DNA and finally rendered completely safe. FIREARMS MUST BE RENDERED SAFE BEFORE SUBMISSION TO THE CRIME LAB. The firearm should be packaged in a cardboard box, envelope, or paper bag separately from the ammunition and/or magazine. The ammunition and/or magazine should be placed in a paper envelope or bag. It is important that the ammunition found in the gun be submitted to the crime lab. Any boxes of similar ammunition found in a suspect's possession should also be placed in a paper container and sent to the crime lab. Cartridges, cartridge cases, and/or bullets found at the crime scene should be packaged separately and placed in paper envelopes or small cardboard pillboxes. If knives (or other sharp objects) are being submitted to the lab (for toolmarks, fingerprints, DNA, etc.), then the blade and point should be wrapped in stiff unmovable cardboard and placed in a paper bag or envelope. The container should be labeled to warn that the contents are sharp and precautions should be taken. This is to prevent anyone from being injured.
SHOEPRINTS AND TIRE TRACKS - can be matched to a pair of shoes or to tires in a suspect's possession. Shoeprints and tire tracks can sometimes tell investigators what type of shoes or tires to look for when searching a suspect's residence or vehicles. Before any attempt is made at collecting shoeprints or tire tracks, natural size photographs should be made using a tripod, ruler, and level. The flash should be held at about 45° angles from the surface containing an impression. Casts can be made of impressions using dental stone. Once hardened, the cast can be packaged in paper and submitted to the lab. When photographing prints on hard flat surfaces the flash should be used as side lighting. Shoeprints on hard flat surfaces can also sometimes be lifted like a fingerprint. Dust prints on certain surfaces can be lifted with gel lifters or an electrostatic dustprint lifter.
FRACTURE MATCHES - can link broken pieces at the scene with pieces found in the possession of a suspect. For example, headlight fragments found at the scene of a hit and run could be matched to a broken headlight (just like putting together a jigsaw puzzle) on a suspect's vehicle. Larger fragments should be placed in paper bags or envelopes. Smaller fragments should be placed in a paper packet and then placed in an envelope.
HAIR - if a root sheath is attached, then DNA analysis can be used to say that the suspect is the source of the hair or the hair came from the suspect with a high degree of probability. If there is no root sheath, then mitochondrial DNA (mtDNA) analysis can be performed in conjunction with a microscopic analysis of the hair to determine if the suspect is a possible source of the hair. With mtDNA and microscopic analyses, unless there is something unique about the hair, no one can say that the hair came specifically from a particular individual. Hair found at the scene should be placed in a paper packet and then placed in an envelope. If a microscopic examination is required, then 15-20 representative hairs from the suspect and victim must be submitted to the lab for comparison. If DNA analysis is going to be used, then a buccal swab or a whole blood sample from the suspect and victim must be submitted to the lab. Contact a DNA lab for more information.
FIBERS - can be said that they are the same type and color as those found in a suspect's clothes, residence, vehicle, etc. Fibers should be collected in a paper packet and placed in an envelope. Reference fibers should be collected and submitted to the lab for comparison.
PAINT - can be said that it is the same type and color as paint found in the possession of a suspect. Paint fragments should be collected in a paper packet and placed in an envelope. Reference paint chips or samples should be collected and submitted to the lab for comparison.
GLASS - can be said that it has the same characteristics as glass found in the possession of a suspect. Smaller glass fragments should be placed in a paper packet and then in an envelope. Larger pieces should be wrapped securely in paper or cardboard and then placed in a padded cardboard box to prevent further breakage. Reference glass samples should be submitted to the lab for comparison.
OTHER TRACE EVIDENCE - during the commission of a crime, there are other items which may be transferred to a perpetrator from the scene or from the perpetrator to the scene (sheetrock, safe insulation, etc.). The guidelines for collecting the evidence and obtaining known samples are the same as for paint and fibers. For specific information, contact your crime lab.