Collection and Preservation of Evidence, Part III (2024)

by George Schiro
Forensic Scientist
Louisiana State Police Crime Laboratory

Once the crime scene has been thoroughly documented and the locations of the evidence noted, then thecollection process can begin. The collection process will usually start with the collection of the most fragileor most easily lost evidence. Special consideration can also be given to any evidence or objects whichneed to be moved. Collection can then continue along the crime scene trail or in some other logicalmanner. Photographs should also continue to be taken if the investigator is revealing layers of evidencewhich were not previously documented because they were hidden from sight.

See also the instructional videos on "Evidence Collection"

Most items of evidence will be collected in paper containers such as packets, envelopes, and bags. Liquiditems can be transported in non-breakable, leakproof containers. Arson evidence is usually collected inair-tight, clean metal cans. Only large quantities of dry powder should be collected and stored in plasticbags. Moist or wet evidence (blood, plants, etc.) from a crime scene can be collected in plastic containersat the scene and transported back to an evidence receiving area if the storage time in plastic is two hours orless and this is done to prevent contamination of other evidence. Once in a secure location, wet evidence,whether packaged in plastic or paper, must be removed and allowed to completely air dry. That evidencecan then be repackaged in a new, dry paper container. UNDER NO CIRc*msTANCES SHOULDEVIDENCE CONTAINING MOISTURE BE PACKAGED IN PLASTIC OR PAPER CONTAINERS FORMORE THAN TWO HOURS. Moisture allows the growth of microorganisms which can destroy or alterevidence.

Any items which may cross contaminate each other must be packaged separately. The containers shouldbe closed and secured to prevent the mixture of evidence during transportation. Each container shouldhave: the collecting person's initials; the date and time it was collected; a complete description of theevidence 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 value of evidence should be kept inmind by the investigator when doing a crime scene investigation. For example, when investigating a crimehe or she should spend more time on collecting good fingerprints than trying to find fibers left by a suspect'sclothing. The reason is that fingerprints can positively identify a person as having been at the scene of acrime, whereas fibers could have come from anyone wearing clothes made out of the same material. Ofcourse if obvious or numerous fibers are found at the point of entry, on a victim's body, etc., then theyshould be collected in case no fingerprints of value are found. It is also wise to collect more evidence at acrime scene than not to collect enough evidence. An investigator usually only has one shot at a crimescene, so the most should be made of it.

The following is a breakdown of the types of evidence encountered and how the evidence should behandled:

Fingerprints

Fingerprints (also includes palm prints and bare footprints) are the best evidence to place an individual atthe scene of a crime. Collecting fingerprints at a crime scene requires very few materials, making it idealfrom a cost standpoint. All non-movable items at a crime scene should be processed at the scene usinggray powder, black powder, or black magnetic powder. Polaroid 665 black and white film loaded in aPolaroid CU-5 camera with detachable flash should be used to make one-to-one photographs of printswhich do not readily lift. All small transportable items should be packaged in paper bags or envelopes andsent to the crime lab for processing. Because of the "package it up and send it to the lab" mentality, someinvestigators skim over collecting prints at a crime scene. Collecting prints at the crime scene should beevery investigator's top priority. Fingerprints from the suspect as well as elimination fingerprints from thevictim will also be needed for comparison (the same holds true for palm and bare footprints).

Bite Marks

Bite marks are found many times in sexual assaults and can be matched back to the individual who did thebiting. They should be photographed using an ABFO No. 2 Scale with normal lighting conditions, sidelighting, UV light, and alternate light sources. Color slide and print film as well as black and white filmshould be used. The more photographs under a variety of conditions, the better. Older bitemarks whichare no longer visible on the skin may sometimes be visualized and photographed using UV light andalternate light sources. If the bitemark has left an impression then maybe a cast can be made of it. Castsand photographs of the suspect's teeth and maybe the victim's teeth will be needed for comparison. Formore information consult a forensic odontologist.

Broken Fingernails

Much like a bullet that has individualizing striations on it, natural fingernails have individualizing striations onthem. A broken fingernail found at a crime scene can be matched to the individual it came from manymonths after the crime has been committed. Broken fingernails should be placed in a paper packet whichis then placed in a paper envelope. It can then be transported to the crime lab for analysis. Knownsamples from the suspect and maybe from the victim will be needed for comparison.

Questioned Documents

Handwriting samples can also be matched back to the individual that produced them. Known exemplars ofthe suspected person's handwriting must be submitted for comparison to the unknown samples. Questioned documents can also be processed for fingerprints. All items should be collected in papercontainers. For more information consult a questioned documents examiner.

Blood and Body Fluids

If using the RFLP method of DNA analysis, then blood and seminal fluid can be matched back to anindividual with a high degree of probability. Currently, if using the PCR method of DNA analysis orconventional serological techniques then blood and some body fluids can be said to come from a certainpopulation group to which the individual belongs. As PCR technology advances, these population groupswill become smaller, eventually giving it the same discriminating power as RFLP analysis has today. Driedblood and body fluid stains should be collected in the following manner: If the stained object can betransported back to the crime lab, then package it in a paper bag or envelope and send it to the lab; if theobject cannot be transported, then either use fingerprint tape and lift it like a fingerprint and place the tapeon a lift back; scrape the stain into a paper packet and package it in a paper envelope; or absorb the stainonto 1/2" long threads moistened with distilled water. The threads must be air dried before permanentlypackaging. For transportation purposes and to prevent cross contamination, the threads may be placedinto a plastic container for no more than two hours. Once in a secure location, the threads must beremoved from the plastic and allowed to air dry. They may then be repackaged into a paper packet andplaced in a paper envelope. 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 tothe 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 itemcannot be transported back to the lab, then absorb the stain onto a small (1"x1") square of pre-cleaned100% cotton sheeting. Package it in paper (or plastic if the transportation time is less than two hours), bringit to a secure place and allow it to thoroughly air dry; then repackage it in a paper envelope. UNDER NOCIRc*msTANCES SHOULD WET OR MOIST ITEMS REMAIN IN PLASTIC OR PAPER CONTAINERSFOR MORE THAN TWO HOURS. Victim and suspect's known whole blood samples will have to becollected in yellow, red, or purple top "Vacutainers." Contact the lab to which the samples will be submittedfor specific information.

Firearms and Toolmarks

Bullets and casings found at the crime scene can be positively matched back to a gun in the possession ofa suspect. Bullets and casings can also be examined at the crime lab and sometimes tell an investigatorwhat make and model of weapons may have expended the casing or bullet. A bullet found at the crimescene can sometimes be matched back to the same lot of ammunition found in a suspect's possession. Toolmarks can be positively matched to a tool in the suspect's possession. Firearm safety is a must at anycrime scene. If a firearm must be moved at a crime scene, never move it by placing a pencil in the barrel orinside the trigger guard. Not only is this unsafe, but it could damage potential evidence. The gun can bepicked up by the textured surface on the grips without fear of placing unnecessary fingerprints on theweapon. Before picking up the gun, make sure that the gun barrel is not pointed at anyone. Keep notes onthe condition of the weapon as found and stops taken to render it as safe as possible without damagingpotential evidence. The firearm can then be processed for prints and finally rendered completely safe. FIREARMS MUST BE RENDERED SAFE BEFORE SUBMISSION TO THE CRIME LAB. The firearmshould be packaged in an envelope or paper bag separately from the ammunition and/or magazine. Theammunition and/or magazine should be placed in a paper envelope or bag. It is important that theammunition found in the gun be submitted to the crime lab. Any boxes of similar ammunition found in asuspect's possession should also be placed in a paper container and sent to the crime lab. Casings and/orbullets found at the crime scene should be packaged separately and placed in paper envelopes or smallcardboard pillboxes. If knives (or other sharp objects) are being submitted to the lab (for toolmarks,fingerprints, serology, etc.), then the blade and point should be wrapped in stiff unmovable cardboard andplaced in a paper bag or envelope. The container should be labeled to warn that the contents are sharpand precautions should be taken. This is to prevent anyone from being injured.

Shoeprints and Tire Tracks

Shoeprints and tire tracks can be matched positively 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 whensearching a suspect's residence or vehicles. Before any attempt is made at collecting shoeprints or tiretracks, one-to-one photographs should be made using a tripod, ruler, and level. The flash should be heldat about 45 degree angles from the surface containing an impression. Casts can be made of impressionsusing dental stone. Once hardened, the cast can be packaged in paper and submitted to the lab. Whenphotographing prints on hard flat surfaces the flash should be used as side lighting. Shoeprints on hard flatsurfaces can also sometimes be lifted like a fingerprint. Dust prints on certain surfaces can be lifted with anelectrostatic dustprint lifter.

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Fracture Matches

Fracture matches can positively link broken pieces at the scene with pieces found in the possession of asuspect. For example, headlight fragments found at the scene of a hit and run could be positively matchedto a broken headlight (just like putting together a jigsaw puzzle) on a suspect's vehicle. Larger fragmentsshould be placed in paper bags or envelopes. Smaller fragments should be placed in a paper packet andthen placed in an envelope.

Hair

If a root sheath is attached, then DNA analysis using PCR technology can say that this hair came from acertain percentage of the population to which the suspect belongs. If there is no root sheath, then amicroscopic analysis can say that the hair has the same characteristics as the suspect's hair and is similarto his or her hair. At this point, no one can say that a hair came from a particular individual. Hair found atthe scene should be placed in a paper packet and then placed in an envelope. If a microscopicexamination is required, then 15-20 representative hairs from the suspect must be submitted to the lab forcomparison. If DNA analysis if going to be used, then a whole blood sample from the suspect must besubmitted to the lab in a "Vacutainer." Contact a DNA lab for more information.

Fibers

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. Representativefibers should be collected from a suspect and submitted to the lab for comparison.

Paint

Paint can be said that it is the same type and color as paint found in the possession of a suspect. Paintfragments should be collected in a paper packet and placed in an envelope. Representative paint chips orsamples should be collected from the suspect and submitted to the lab for comparison.

Glass

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 piecesshould be wrapped securely in paper or cardboard and then placed in a padded cardboard box to preventfurther breakage. Representative samples from the suspect should be submitted to the lab for comparison.

Other Trace Evidence

Sometimes during the commission of a crime, there are other items which may be transferred to aperpetrator from the scene or from the perpetrator to the scene (sheetrock, safe insulation. etc.). Theguidelines for collecting the evidence and obtaining known samples is about the same as for paint andfibers. For specific information, contact your crime lab.

RECOMMENDED READING:

• "Evidence Handling Guide" LA. Dept. of Public Safety and Corrections, Office of State Police, Crime Laboratory

• Continue to Part IV--Special Considerations for Sexual Assault Evidence