When recovering biological evidence from a crime scene it must be handled with extreme caution, as it is highly perishable. This article discusses the recovery of hair and semen from bedding and clothing left at the scene after a sexual assault. After an initial search of the scene—done to locate the evidence—the evidence should be well photographed and videotaped. Also, it should be noted that investigators must wear protective clothing—at all times, no matter what evidence is being collected—changing them every time new evidence is collected, as well as using tools, such as tweezers and so on.
The clothing of the victim can contain vital clues, such as trace material and biological evidence. Careful documentation of where the clothes were found is important. Clothing should be examined at the scene by forensic analysts, using a UV Light, Blue Light, or Forensic Light source to identify stains. All biological evidence should be air-dried before being packaged. Likewise, bed linens should be in the same manner. If there are stains, they should be marked, air dried, then packaged by folding the edges toward the center and placed in a paper bag. It is vital that investigators avoid coughing, sneezing, and avoid touching their faces and other areas of their body’s that might aid in contamination of the sample collected. All stains collected should be accompanied by a control sample, which can be obtained from an unstained area near the collected stain. Each item of semen evidence should be packaged separately, and if transport of the entire item—such as the whole bed—a portion around where the stain is located should be cut out and sent to the lab, for practical purposes. All biological evidence should be transported at room temperature.
All hair should be recovered from a scene. Hair should be collected using gloved fingers or tweezers, placed in paper bindles or coin envelopes, then placed in larger envelopes, which should be folded and sealed, then labeled by the crime scene investigator. All biological evidence must be packaged in paper bags or other “breathable containers” and not airtight containers, which can cause growth of bacteria that can degrade the evidence. The basic rule that most lab assistants follow for storage of biological evidence is to refrigerate wet or liquid evidence and freeze dry evidence. After a barcode is placed on the item, and corresponding bar code is place on the property receipt, all DNA material should be placed into a designated biohazard area.
In the Lab
Human hair can not only be inspected by tested for DNA; it can also be compared to other hair samples in order to determine whether or not two samples could have had a common origin (by use of a comparison microscope). Using various testing methods at the lab, such as the restriction fragment length polymorphism (RFLP) process or the polymerase chain reaction (PCR) process, DNA can be extracted from semen, which can be examined and amplified in order to determine the genetic profile of the individual who left it behind. Of course, if it is the suspect’s semen, and no samples to compare it to, it should be held for safe keeping, and hopefully investigators will find a suspect; at which time, the investigators can take a DNA sample from the suspect and compare it to the earlier collected sample.
Of course, once the original sample is collected, investigators can first check the DNA data base run by the FBI, known as the Combined DNA Index System (CODIS). The CODIS system is an electronic database that houses DNA profiles that can identify suspects. As of April of 2012, CODIS contained over 10 million offender profiles (NDIS Statistics, 2012).