Forensic Biology is the analysis of body fluids, stains and other bodily materials to help solve a crime. Typically, this involves the positive identification of blood, semen, or saliva and further genetic testing (DNA) to determine who the material may have originated from, typically the alleged victim, suspect or other involved party.
Some laboratory systems expect the Forensic Biologist to handle all evidence in their area from a given case from “cradle to grave”, i.e from initial detection to identification and DNA testing and prosecution. Some use an “assembly line” approach, where one scientist may do only evidence screening, which means they only look for the body fluids, another would do tests to determine what the fluids are, and yet another would do DNA analysis. This approach allows the scientist to focus on a single area of expertise, although the “cradle to grave” approach gives a better overall understanding of the case and what may or may not be important based on related factors.
Depending on the agency or company you work for, you therefore may be trained in a variety of biological techniques or possibly just a single specialty, like DNA analysis. Some agencies also expect their scientists to go to the crime scene and collect evidence Most, however have crime Scene Technicians dedicated to this task. The evidence is then transported to the laboratory for analysis.
A Forensic Biologist usually begins their analysis by examining a piece of evidence for the presence of hairs, fibers and stains. Any collected hairs or fibers of evidential value are most often transferred to a Forensic Microscopist for further analysis. However, it is usually the job of the Forensic Biologist to collect and preserve the hairs and fibers initially.
Many times an alternate light source, such as a laser is used to find stains on articles such as bed sheets or clothing. A portion of the stain is removed and tested for identification. The most common types of test are those for blood and semen, although at times it is necessary to test for other body fluids or tissues such as urine or saliva. A forensic scientist must know not only how to perform the appropriate test, but also how to interpret the results. Some tests can provide absolute answers, for instance, if a stain is in fact blood. Others can only provide a “likely” answer, like in the case of saliva, where there is no absolute conclusion. A positive analysis for this type of test means only that a substance is indicated (probable), not conclusively identified. Overstating conclusions is always a risk for the poorly trained or over confident Forensic Biologist.
Once a stain is identified, the scientist is often asked to determine who it could or could not have originated from. For example, if blood is found in a car, it may be beneficial to the case to find out if it originated from a people thought to be involved in the case, usually a victim and suspect. In this scenario, DNA analysis would be conducted on the blood in the “questioned stain” to develop a DNA profile. The questioned profile would then be compared to the known DNA profiles of the victim and suspect. If the profiles are the same, the are considered a “match” and the next step is to figure out what that match means. How many other people could be expected to have the same profile? Depending on amount of detail discovered in the DNA profile, this could range from a lot of people, to one in several billion, or essentially only a single person. With this type of strong match, DNA analysis if very similar to a fingerprint, and the analyst is able to testify in court that the blood originated from specific individual.