by George Schiro
Louisiana State Police Crime Laboratory
The most important aspect of evidence collection and preservation is protecting the crime scene. This is to keep the pertinent evidence uncontaminated until it can be recorded and collected. The successful prosecution of a case can hinge on the state of the physical evidence at the time it is collected. The protection of the scene begins with the arrival of the first police officer at the scene and ends when the scene is released from police custody.
All police departments and sheriff's offices should include intensive training for its personnel on how to properly protect crime scenes. Potentially, any police officer can be put into the position of first responding officer to a crime scene. The first officer on the scene of a crime should approach the scene slowly and methodically. In some eases this is not altogether practical. The first officer may also be involved in arresting an uncooperative suspect or performing life saving measures on an injured victim. In either ease the officer should make mental or written notes (as is practical in each situation) about the condition of the scene as it was upon the officer's arrival and after the scene has been stabilized. The officer should keep notes on the significant times involved in responding to the crime scene (time dispatched to scene, time left for scene, time arrived at scene, time left scene, etc.). An effort must be made to disturb things as little as possible in assessing the situation. Particular attention should be paid to the floor since this is the most common repository for evidence and it poses the greatest potential for contamination. Notes should also be taken if the officer has to alter something in the investigation. Some things the officer should note include: the condition of the doors, windows, and lighting (both natural and manmade); if there are any odors present; if there are any signs of activity; how EMS or fire personnel have altered the scene; anything essential about the suspect (description, statements, physical condition, mental condition, intoxication, etc.); and anything essential about the victim. Once the scene has been stabilized, the scene and any other areas which may yield valuable evidence (driveways, surrounding yards, pathways, etc.) should be roped off to prevent unauthorized people from entering the area and potentially contaminating it. Investigators and other necessary personnel should be contacted and dispatched to the scene, however, under no circumstances should the telephone at the scene be used. Once the officer has secured the scene, he or she could do the following: record witness names and others who may have entered or been at the scene; separate witnesses and suspect(s); do not discuss the events or the crime with witnesses or bystanders or let the witnesses discuss these events; listen attentively but discreetly; and protect evidence which may be in danger of being destroyed. Any actions taken should be reported to the investigators.
Many times the arrival of additional personnel can cause problems in protecting the scene. Only those people responsible for the immediate investigation of the crime, the securing of the crime scene, and the processing of the crime scene should be present. Non-essential police officers, district attorney investigators, federal agents, politicians, etc. should never be allowed into a secured crime scene unless they can add something (other than contamination) to the crime scene investigation. One way to dissuade unnecessary people from entering the crime scene is to have only one entrance/exit into the crime scene. An officer can be placed here with a notebook to take the names of all of the people entering the crime scene. The officer can then inform them that by entering the crime scene they may pose a problem by adding potential contamination, and the reason that the officer is taking their names is in case the crime scene investigators need to collect fingerprints, shoes, fibers, blood, saliva, pulled head hair, and/or pulled pubic hair from all those entering the crime scene. This will sometimes discourage non-essential personnel from entering the crime scene. The officer can also stop unwanted visitors from entering the restricted areas. If extraneous people do have to enter the scene, then make sure that they are escorted by someone who is working the scene. This is to make sure that they will not inadvertently destroy any valuable evidence or leave any worthless evidence.
Eating, drinking, or smoking should never be allowed at a crime scene. Not only can this wreck a crime scene but it can also be a health hazard. A command post should be set up for such purposes. The post is to be set up somewhere outside the restricted areas. It could be a vehicle, picnic table, hotel room, tent, etc. It can be used as a gathering place for non-involved personnel, a place for investigators to take breaks, eat, drink, or smoke, a communication center, a place for press conferences, a central intelligence area, etc. The best thing about it is that it is away from the crime scene.
Protection of the crime scene also includes protection of the crime scene investigators. One person, whether a civilian or a police crime scene investigator, should never be left alone while processing the scene. This is especially true if the suspect has not been apprehended. There are many stories of suspects still hiding at or near their area of misdeed. That is why there should always be at least two people working the scene. At least one of these people should have a radio and a firearm.
Examination of the Crime Scene
Before the investigators begin examining the scene of the crime, they should gather as much information as possible about the scene. Once again, a slow and methodical approach is recommended. Information is gathered to prevent destruction of valuable and/or fragile evidence such as shoeprints, trace evidence, etc. Once all of the information is gathered, a mental plan is formulated as to how the crime scene will be analyzed. Copious notes and relevant times should be kept on every aspect of the crime scene investigation. The examination of the scene will usually begin with a walk through of the area along the "trail" of the crime. The trail is that area which all apparent actions associated with the crime took place. The trail is usually marked by the presence of physical evidence. This may include the point of entry, the location of the crime, areas where a suspect may have cleaned up, and the point of exit. In some cases, a walk through may become secondary if potential evidence is in danger of being destroyed. In that case, this evidence should be preserved, or documented and collected as quickly as possible.
The purpose of the walk through is to note the location of potential evidence and to mentally outline how the scene will be examined. The walk through begins as close to the point of entry as possible. The first place the investigators should examine is the ground on which they are about to tread. If any evidence is observed, then a marker should be placed at the location as a warning to others not to step on the item of interest.
A good technique to use indoors on hard floors is the oblique lighting technique (also known as side lighting). A good flashlight with a strong concentrated beam is the only tool needed. The room should be darkened as much as possible. If a light switch which a suspect may have touched needs to be turned off, then make sure the switch has been dusted for fingerprints first. Do not close any blinds or shades until after all general photographs have been taken. In the side lighting technique, a flashlight is held about one inch from the floor. The beam is then angled so that it just sweeps over the floor surface and is almost parallel to the surface. The light is then fanned back and forth. Any evidence, such as trace evidence and shoeprints, will show up dramatically. Under normal lighting conditions, this evidence may be barely visible or completely invisible.
As the walk through progresses, the investigators should make sure their hands are occupied by either carrying notebooks, flashlights, pens, etc. or by keeping them in their pockets. This is to prevent depositing of unwanted fingerprints at the scene. As a final note on the walk through, the investigators should examine whatever is over their heads (ceiling, tree branches, etc.). These areas may yield such valuable evidence as blood spatters and bullet holes. Once the walk through is completed, the scene should be documented with videotape, photographs, and/or sketches.
Documenting the Crime Scene
Videotaping the Crime Scene
If available, a video camera is the first step to documenting a crime scene. Videotape can provide a perspective on the crime scene layout which cannot be as easily perceived in photographs and sketches. It is a more natural viewing medium to which people can readily relate, especially in demonstrating the structure of the crime scene and how the evidence relates to the crime. The video camera should have a fully charged battery as well as date and time videotape display functions. A title generator and "shake free" operations are also nice options. If a title generator is not available, then about 15 seconds at the beginning of the tape should be left blank. This will allow the addition of a title card with any pertinent information to the beginning of the crime scene tape. The condition of the scene should remain unaltered with the exception of markers placed by the investigators and any lights turned on during the walk through. These alterations can be noted on the audio portion of the tape. Before taping, the camera range should be cleared of all personnel. Any people in the area should be forewarned that taping is about to commence and they should remain silent for the duration of the tape. This prevents recording any potentially embarrassing statements.
Once the video camera begins recording, it should not be stopped until the taping is complete. The key to good videotaping is slow camera movement. A person can never move too slowly when videotaping, yet it is all too easy to move the camera fast without realizing it. This is why videotaping is not ideal for viewing detail. People have a tendency to pan past objects in a manner that does not allow the camera to properly capture the object. This is why slow panning of an area is necessary and it should be panned twice in order to prevent unnecessary rewinding of the tape when viewing.
The taping should begin with a general overview of the scene and surrounding area. The taping should continue throughout the crime scene using wide angle, close up, and even macro (extreme close up) shots to demonstrate the layout of the evidence and its relevance to the crime scene. If videotaping in a residence, the camera can show how the pertinent rooms are laid out in relation to each other and how they can be accessed. This is sometimes lost in photographs and sketches. After the taping is complete, it is wise to leave about 15 seconds of blank tape to prevent the crime scene tape from running into anything else previously recorded on the tape. The tape should then be transferred to a high quality master tape. The recording tabs should be removed from the master tape after transferring the crime scene tape and the master should be stored in a safe place. This is to prevent accidental erasure of the crime scene tape. Copies can then be made from the master tape.Still Photography
Whether a video camera is available or not, it is absolutely essential that still photographs be taken to document the crime scene. If a video camera is available, then photographs will be the second step in recording the crime scene. If video is not available, then still photography will be the first step. Photographs can demonstrate the same type of things that the videotape does, but photographs from the crime scene can also be used in direct comparison situations. For example, actual size photographs (also known as one-to-one photos) can be used to compare fingerprint and shoeprints photographed at the crime scene to known fingerprints or shoes from a suspect. This is the advantage of photographs over videotape.
Almost any type of camera with interchangeable lenses and a format of 35mm or larger will do in crime scene photography. The lenses should include a 28mm wide angle lens, a normal 55mm lens, and a lens with macro capabilities (1:4 or better). The flash unit used with the camera should be one that is not fixed to the camera. It should be able to function at various angles and distances from the camera. This is to allow lighting of certain aeras to provide maximum contrast, place the flash in hard to reach areas, and reduce flash wash out which can render the item photographed invisible. Print and/or slide color film (25-400 ISO) should be used. A tripod, a level, and a small ruler should also be available for one-to-one photography. It may be of help to the investigation to have a Polaroid camera handy for instant photographs. For example, an instant photograph of a shoeprint found at a crime scene can be provided to investigators who are running a search warrant on a suspect's residence. The photo will tell them the type of shoe for which they are searching.
The photography of the crime scene should begin with wide angle photos of the crime scene and surrounding areas. When shooting the general overall scene, the photos should show the layout of the crime scene and the overall spatial relationships of the various pieces of evidence to each other. A good technique to use indoors is to shoot from all four corners of a room to show its overall arrangement. The next set of photos should be medium range to show the relationships of individual pieces of evidence to other pieces of evidence or structures in the crime scene. Finally, close up photos should be taken of key pieces of evidence. A ruler should be photographed with items where relative size is important or on items which need to have one-to-one comparison photographs. The object should first be photographed as is, then photographed with the ruler. It is important that when doing one-to-one photography that the ruler is on the same plane as the object being photographed and the film plane is parallel to the ruler. This is why a level and a tripod are necessary. Notes should also be taken as to what the investigator is photographing or wishes to demonstrate in each photograph. This is to prevent the investigator from getting the picture back at a later date and trying to figure out what he or she was trying to accomplish with the photo. The same areas should be photographed in the same sequence as mentioned above in the paragraphs on videotaping.Crime Scene Sketching
The final phase in documenting the scene is making a crime scene sketch. The drawback of photographs is that they are two-dimensional representations of three-dimensional objects. As a result, most photographs can distort the spatial relationships of the photographed objects causing items to appear closer together or farther apart than they actually are. If spatial relationships of the evidence are important or if something needs to have proportional measurements included in it for calculations (such as bullet trajectory angles, accident reconstructions, etc.) then a sketch must be made of the crime scene.
A sketch is usually made of the scene as if one is looking straight down (overhead sketch) or straight ahead (elevation sketch) at a crime scene. A rough sketch at the scene is usually made first on graph paper in pencil with so many squares representing so many square feet or inches. Directionality of the overhead view is determined by using a compass. Using a tape measure or other measuring devices, measurements are taken at crime scene of the distances between objects and/or structures at the crime scene. These measurements are proportionally reduced on the rough sketch and the objects are drawn in. Two measurements taken at right angles to each other or from two reference points will usually suffice in placing the objects where they belong in a sketch. Double measurements should also be taken to make sure they are correct. This is especially true where calculations will later be used. A final sketch can be made later using inks, paper, and ruler, or a computer. The original rough sketch should be retained and preserved in case it is needed at a later date. Once the scene has been thoroughly documented then the evidence collection can commence.
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 or most easily lost evidence. Special consideration can also be given to any evidence or objects which 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 which 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, leakproof 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. 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 PACKAGED IN PLASTIC OR PAPER CONTAINERS FOR MORE THAN TWO HOURS. Moisture allows the growth of microorganisms which can destroy or alter evidence.
Any items which may 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 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 value of evidence should be kept in mind by the investigator when doing a crime scene investigation. For example, when investigating a crime he or she should spend more time on collecting good fingerprints than trying to find fibers left by a suspect's clothing. The reason is that fingerprints can positively identify a person as having been at the scene of a crime, whereas fibers could have come from anyone wearing clothes made out of the same material. Of course if obvious or numerous fibers are found at the point of entry, on a victim's body, etc., then they should be collected in case no fingerprints of value are found. 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
Fingerprints (also includes palm prints and bare footprints) are the best evidence to place an individual 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 should be used to make one-to-one photographs of prints which do not readily lift. All small transportable items should be packaged in paper bags or envelopes and sent to the crime lab for processing. 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).Bite Marks
Bite marks are found many times in sexual assaults and can be matched back to the individual who did the biting. They should be photographed using an ABFO No. 2 Scale with normal lighting conditions, side lighting, UV light, and alternate light sources. Color slide and print film as well as black and white film should be used. The more photographs under a variety of conditions, the better. Older bitemarks which are no longer visible on the skin may sometimes be visualized and photographed using UV light and alternate light sources. If the bitemark has left an impression then maybe a cast can be made of it. 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
Much like a bullet that has individualizing striations on it, natural fingernails have individualizing striations on them. A broken fingernail found at a crime scene can be matched to the individual it came from many months after the crime has been committed. 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 samples 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 of the 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 paper containers. 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 an individual with a high degree of probability. Currently, if using the PCR method of DNA analysis or conventional serological techniques then blood and some body fluids can be said to come from a certain population group to which the individual belongs. As PCR technology advances, these population groups will become smaller, eventually giving it the same discriminating power as RFLP analysis has today. Dried blood and body fluid stains should be collected in the following manner: If the stained object 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 either use fingerprint tape and lift it like a fingerprint and place the tape on a lift back; scrape the stain into a paper packet and package it in a paper envelope; or absorb the stain onto 1/2" long threads moistened with distilled water. The threads must be air dried before permanently packaging. For transportation purposes and to prevent cross contamination, the threads may be placed into a plastic container for no more than two hours. Once in a secure location, the threads must be removed from the plastic and allowed to air dry. They may then be repackaged into a paper packet and placed 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 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 a small (1"x1") square of pre-cleaned 100% cotton sheeting. 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 IN PLASTIC OR PAPER CONTAINERS FOR MORE THAN TWO HOURS. Victim and suspect's known whole blood samples will have to be collected in yellow, red, or purple top "Vacutainers." Contact the lab to which the samples will be submitted for specific information.Firearms and Toolmarks
Bullets and casings found at the crime scene can be positively matched back to a gun in the possession of a suspect. Bullets and casings can also be examined at the crime lab and sometimes tell an investigator what make and model of weapons may have expended the casing or bullet. A bullet found at the crime scene 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 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. The gun can be picked up by the textured surface on the grips without fear of placing unnecessary fingerprints on the weapon. Before picking up the gun, make sure that the gun barrel is not pointed at anyone. Keep notes on the condition of the weapon as found and stops taken to render it as safe as possible without damaging potential 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 firearm should be packaged in an 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. Casings 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, serology, 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
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 when searching a suspect's residence or vehicles. Before any attempt is made at collecting shoeprints or tire tracks, one-to-one photographs should be made using a tripod, ruler, and level. The flash should be held at about 45 degree 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 an electrostatic dustprint lifter.Fracture Matches
Fracture matches can positively 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 positively 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 using PCR technology can say that this hair came from a certain percentage of the population to which the suspect belongs. If there is no root sheath, then a microscopic analysis can say that the hair has the same characteristics as the suspect's hair and is similar to his or her hair. At this point, no one can say that a hair came 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 must be submitted to the lab for comparison. If DNA analysis if going to be used, then a whole blood sample from the suspect must be submitted 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. Representative fibers 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. Paint fragments should be collected in a paper packet and placed in an envelope. Representative paint chips or samples 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 pieces should be wrapped securely in paper or cardboard and then placed in a padded cardboard box to prevent further 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 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 is about the same as for paint and fibers. For specific information, contact your crime lab.
When dealing with sexual assaults, the investigator usually has a living victim who can provide the investigator with information which will help in collecting and preserving the pertinent evidence. The investigator should glean as much information as possible, so he or she will know which evidence to collect. For example, if the victim tells the investigator (which in this case may be the examining physician) that no oral penetration occurred, then the investigator knows that no oral swabs will need to be taken. Any information should be passed on to the crime lab, so the forensic scientists will know how to process the evidence submitted. Evidence should never be submitted without communicating relevant information.
When dealing with sex crimes, the victim should be taken to the hospital immediately and the examination started as soon as possible. Photographs should be taken to document any injuries which the victim received. If necessary, oral, vaginal, and/or anal swabs should be taken from the victim and air dried for one hour in a moving air source as soon as possible. They should be collected as soon as possible because the body begins breaking down the various components in seminal fluid through drainage, enzyme activity, pH, etc. The swabs should be air dried under a fan for at least one hour. This can either be accomplished by the doctor at the hospital, or, upon collecting the kit from the doctor, the investigator should bring it immediately to a secure place and air dry it. The reason for this is that the moisture in the swabs allows microorganisms to grow which can destroy the evidentiary value of the swabs. Known saliva samples from the victim must also be air dried along with any other wet or moist samples (not including whole blood samples, vaginal washing or any other liquid samples collected).
Usually, the best sample of seminal fluid comes from the swabs, as long as they are preserved properly. The next best place is usually the victim's panties because the seminal fluid will drain into the panties (if the assault was vaginal or anal in nature). The stain will sometimes be better preserved because the seminal fluid tends to dry faster in the panties. If the panties have wet stains, then they should be air dried as soon as possible before packaging. Clothes can be a good source of seminal fluid if the assailant ejaculated on the victim's clothes. The clothes can also be a source for the suspect's blood, hairs, fibers, or other evidence transferred to the victim from the suspect. Clothing should be air dried before permanent packaging and each article of clothing should be packaged separately.
Bed sheets, comforters, spreads, etc. can also be a source of evidence from the suspect. The value of this type of evidence should be carefully considered by the investigator before collecting it. If the bed is a "high traffic" area, meaning that numerous people have had access to the bed and the bed sheets haven't been cleaned in a long time, then it won't have as much evidentiary value as a bed where only one person had access to it and the sheets have been cleaned recently. The investigator should use the side lighting technique to look for any loose trace evidence on the sheets which may be lost during handling and packaging. This evidence should be placed in a paper packet and then placed in an envelope. If the sheets have wet stains and these can be attributed to the rape, then the investigator should circle these stains and inform the crime lab that those are the relevant stains to be examined. The investigator should note that he or she circled the stains and as always, air dry the evidence before permanently packaging it. The investigator should neatly fold the sheets inward to prevent the loss of any other loose evidence. The sheets can then be packaged separately in paper bags, air dried if necessary, and submitted to the crime lab.
If a suspect is established in a rape case, then reference samples should be collected from the suspect for comparison. These samples should include: a whole blood sample in a red, yellow, or purple top "Vacutainer"; a saliva sample (air dried); 15-20 pulled head hairs; and 15-20 pulled pubic hairs. If the suspect is captured within 24 hours and it can be established which clothes and/or shoes he wore during the attack, then the items should be packaged separately and submitted to the crime lab. Sometimes trace evidence from the victim such as hairs, fibers, blood, etc. can be found on the suspect's clothing.
The key to proper collection, preservation, analysis, and overall usefulness of evidence is open and plentiful communication between investigators, forensic scientists, and prosecutors. This will make the most of the evidence which can make or break a case. This paper has presented general guidelines on the collection and preservation of evidence. The investigator should remember that each crime scene is different and each crime scene is a learning process. The investigator should also keep in mind that different crime labs may like their evidence collected in different manners. This is why the investigator should not hesitate to call his or her crime lab if he or has a question or a problem on the collection or preservation of evidence.
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