Sexual Assault Presentation
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- Length: 1444 words (4.1 double-spaced pages)
- Rating: Excellent
Ms. St. Pierre began her discussion with an overview of the fundamentals of criminalistics and serology, before moving into more depth. It can be used to identify these biological substances that are treated as evidence. The ultimate goal of evidence processing is to establish a link. There are many pieces to the puzzle both biologically and event-wise that fit in the scene. Beginning with examination, she stressed the importance of tests that range in levels of intimacy such as victim’s personal account, to examining the victim’s whole body. Every piece of evidence from the corroboration of the victim’s account to biological swab testing is vital when tying everything together and establishing a good case. When discussing the Sexual Assault Evidence Collection Kit, she explained how many things could be processed. She highlighted swabs and microscopic smear slides, which could be important for determining a timeline. She also mentioned blood, hair combings, fingernail scrapings and clothing as important pieces of evidence that must be processed. She even once described a time where she received an entire bag of hair as evidence. She claimed it was the oddest piece of evidence she ever received, but it would definitely help with biological examination. Once preserving items that are removed from the crime scene and/or victim, the evidence is then brought to the lab for identification towards the purpose of establishing the link.
As enforced by Ms. St. Pierre and Detective Goff, preservation of evidence is vital to avoid confusion that can ultimately work against a prosecution. Garments should be gathered in paper bags to preserve possible biological evidence. As a biological substance, blood must be preserved carefully. An anticoagulant must be added to blood to keep it from clotting as well as a preservative to keep microorganisms from growing in the blood. Blood or bodily fluids must be air-dried to keep them from being altered and preserved in a refrigerator or freezer. Items are usually kept at room temperature, cooled, or frozen depending on the amount of time they need to be preserved prior to examination.
Ms. St. Pierre started discussing specific biological evidence processing with blood. She gave the basic outline that blood is composed of cells, enzymes and proteins, but she also began to outline the role of antigens and antibodies in the blood. She outlined three different kinds known as A, B and O. Using the lock-and-key model, she explained that red blood cells that contain A antigens that clump together with A antibodies and do not combine with B antibodies. The O blood type contains neither A and B antigens and thus combines with both. These groups can be identified by testing a sample thought to be blood with anti-A and Anti-B sera.
If it is encountered at the crime scene, investigators and scientists cannot call the possible substance blood. Until screening and confirmatory tests are performed, Ms. St. Pierre explained that she and all of her peers referred to the substance as “a reddish brown staining.” She showed multiple ways to test for blood and the pros and cons of each. Like the process of drug identification, a color test is a valuable screening test for blood, but it does not confirm the substance. She referred to these kinds of tests as, “Presumptive.” Fluorescence tests such as Bluestar or Luminol that merely reveal the reddish brown stains and indicate blood would also qualify as presumptive tests, for they are not able to discern the material. Color tests would also be known as a presumptive test. Confirmatory tests would include microcrystalline tests and immunoassay tests. Microcrystalline tests involve looking for characteristic crystals from the hemoglobin, while immunoassay tests using HemaTrace Cards detect human hemoglobin in the reddish brown stain.
In the matter of sexual assault, semen examination is a vital component that can make or break a case. But which tests can confirm it’s presence? At a crime scene (and commonly seen in many crime TV dramas), an alternate light source can be used to illuminate evidence. At approximately 450nm some biological fluids do emit fluorescence such as semen and saliva, but Ms. St. Pierre explained that a definite confirmation cannot be made. While we can see semen and saliva using an ALS, other non-biological fluids such as laundry detergent look very similar so more extensive testing is needed. Ms. St. Pierre highlighted another way to characterize a semen stain is by performing an acid phosphatase color test. She explained acid phosphatase as an enzyme located in seminal fluid, which can be identified if it comes into contact with different dyes. Microscopic examination is a confirmatory test, specifically the identification of spermatazoa, the sperm cells. Ms. St. Pierre explained that there are approximately 100 million sperm cells per milliliter of ejaculate and 2.5-5 mL of ejaculate per “session.” Using a picture example of what a semen sample would look like under a microscope, Ms. St. Pierre broke away from her formal and scientific language to say, “the epithelial cells look fried eggs and the little red ones are sperm cells.” Crude but effective vocabulary definitely helped lighten the mood of the overall discussion and when looking at the photo, many of us chuckled when we realized she was right.
However Ms. St. Pierre did inform us that there are some cases where no sperm cells will be found in a sample, and while that may cause some suspicion, she pointed out that this does not invalidate the evidence. She outlined different infertility disorders such as ogliospermia (low sperm count) and aspermia (no sperm count) and standard procedures such as vasectomies that can lead to no sperm cells being found. So if there is no sperm cells in a sample how can we prove that there is semen present? Along with the acid phosphatase test, Ms. St. Pierre also showed how a p30 antigen (PSA) test can identify semen. If the stain is placed opposite anti-p30 and an electrical potential is added, the antigens and antibodies move and if a visible line is shown midway between the two, it indicates the presence of the p30 antigen.
According to Ms. St. Pierre, saliva is not uncommon at crime scenes involving sexual assault, often on the victim. As a mixture containing water, amylase and other substances such as buccal cells (cheek cells that can be used for gathering DNA), saliva is an important piece of biological evidence that an tie a victim to the crime scene. When testing for saliva, radial diffusion is used as a presumptive test while once more, immunoassay is confirmatory. Radical diffusion tests for the presence of amylase using a starch iodine test. The presumptive test is based off the saliva amylase’s ability to break down starch. The sample is stained with iodine, and starch reacts to the iodine, turning blue. When dealing with the radical diffusion specifically, the starch is prepared in agar gel. When the iodine is poured over the gel and the unknown sample is added to separate wells in the gel, the starch diffuses and breaks down. The voided areas where the starch has broken down are proportional to the amount of amylase present in the unknown sample.
Ms. St. Pierre explained that he DNA recovered is then taken to CODIS. CODIS Stands for Combined DNA Index System and it is a database of crime scene samples from convicted felons, missing persons, and more. DNA can be pulled from biological material such as blood, semen, saliva and skin cells. So there must be reference samples to confirm any “hit” on CODIS. DNA CODIS itself can be another link, connecting case to case or case to offender.
Both before and after the evidence is processed, Detective Goff is on the move. As a detective specializing in the processing of sexual assault and battery, it is Detective Goff’s job to step into the outside world and communicate with the people involved in these matters. In cases of sexual assault, the victim has a choice on whether or not they want to pursue the case. Depending on the nature of the crime and the evidence, the district attorney may decide to pursue the case, but sadly, it is not common to see victims decide not to press charges for cases of sexual assault. With a slightly callous attitude (mostly due to years of rather gruesome experience) Detective Goff pointed out that many victims are “on the fringe” meaning they are drug users, homeless and as such often difficult to track down after the initial report.
Overall, the speakers provided preliminary information about how sexual assault cases are examined and processed. The two different perspectives really highlighted the difference that specific occupation has on the overall attitude towards the case and how many scientific methods are implemented in cases like these everyday. It was a very informative and illuminating discussion.
Saferstein, Richard. PhD Criminalistics: An introduction to Forensic Science. 10th Ed. Prentice Hall. 2011. P.4