CSI And Sexual Assault
CSI And Sexual Assault
Richard Saferstein (Former Chief Forensic Scientist) gives expert video advice on: How has forensic science changed sexual-assault crime investigation?; How is semen studied in CSI?; What evidence from the victim of a sexual assault is studied in CSI? and more...
How has forensic science changed sexual-assault crime investigation?
Three letters to that answer: DNA. Prior to the advent of DNA analysis, the forensic community really had no definitive way of tying a suspect rapist into an assault. And when DNA came along, the DNA fingerprinting technique allowed us to identify deposition of semen and hairs at scenes of sexual assaults with a particular individual. So DNA has really changed the complexity of sexual assault investigations.
How is semen studied in CSI?
There are a number of tests. Perhaps the first test that is most important to use is locating the stain. This is done with a color test known as the acid phosphatase color test. Acid phosphatase is an enzyme that is present in human seminal fluid. It is present in high concentrations, and it is locatable through this color test known as the acid phosphatase color test. If semen is located, the next test is to look for spermatozoa. This is a specific test, and the stain will be examined under a microscope for the presence of human sperm. However, often, spermatozoa are not to be found, for a number of reasons, so the next test that we would use would be the prostate-specific antigen test known as the PSA test. It is the same test that is used for medically testing individuals for the presence of prostate cancer. The PSA test is a very specific test for human seminal fluid, and serves as an identifier in place of human sperm. Finally, we have a DNA test. If we have identified the stain as being seminal in nature, as being sperm or PSA, the presence of DNA will allow us to link that stain to one, and only one, individual.
What evidence from the victim of a sexual assault is studied in CSI?
When a sexual assault occurs, the victim is brought to a medical facility where certain items of evidence are collected. Specifically vaginal swabs, anal swabs and oral swabs. In addition, the victim's pubic hair area is combed to collect any foreign hairs or debris that may be present. Collections are made of the head hair controls from the victim, as well as the pubic hair controls as well. Of course, all of the clothing from that victim is gathered up and sent to the crime lab. What's also important is a search for drugs. On some occasions, the victim may be drugged. By collecting blood and urine, the forensic toxicologist can look for the presence of these types of substances. And of course we can't forget DNA. We must have the DNA type of the victim, and this would be obtained through what we call a bugle swab. That is swabbing the inner surface of the cheek to collect cells that would ultimately be used to identify that victim's DNA.
What evidence from the suspect in a sexual assault is studied in CSI?
Often the suspect is not apprehended until many hours, perhaps even a few days, if that, after the assault has taken place. If the suspect is apprehended, of course a DNA sample must be obtained through a bugle swab. Interestingly enough if the suspect is nabbed within 24 hours of the assault it is recommended that penile swabbings be taken from the suspect because the vaginal cells can remain on the male penis for up to 24 hours. Hair samples would be taken: pubic hair samples and head hair samples for control purposes. And of course all of the clothing the suspect was thought to have worn on the night or the day of the assault is collected and sent off to the crime lab as well.
When should a victim of a sexual assault report the crime?
As quickly as possible. One of the problems that we have currently in terms of the science of forensics is the inability to detect drugs that are often used to induce a female into sexual activity. These drugs normally disappear from the human body within 24 hours. If we, we being the investigators, can collect urine or blood from the victim within 24 hours, the ability to detect those drugs may be lost.