The Forensic Evidence Lab Procedure on Blood, Semen and Saliva Found at a Crime Scene

The Forensic Evidence Lab Procedure on Blood, Semen and Saliva Found at a Crime Scene

The art of forensic science is treasured and trusted to deliver competent evidence required to tie a suspect to a particular crime scene. It also helps exonerate an innocent suspect held in custody. Following a guided step by step analysis of the provided evidence, forensic science utilizes some tiny critical details to unveil the identity, tally, the positioning of the people present at the scene (Peterson, Sommers, Baskin, & Johnson, 2010). This paper outlines the specific process entailed in a laboratory processing of the blood, semen, and saliva found at a crime scene to deduct a given verdict from what is proven.

The collection, storage, transportation, and handling of the evidence involved in a crime scene is critical. If specified measures are not in the whole process concerning the evidence, then the evidence could lose crucial forensic information (Budowle, 2006). The collection of these evidence samples should be as simple as possible, able to prevent any form of degradation, and on top of that ensure minimization of contamination with other biological samples. The objects that pertain the samples play a significant role in deciding what method to use in the collection and transportation of the evidence. Portable objects like the broken glass, clothing, and drinking glasses are more efficient when carried individually to the laboratory to test for blood, semen, or saliva involved. The carpet portion containing the blood is preferably cut out and the part with the DNA evidence packaged for transportation. Swabbing is used to collect the blood evidence on the furniture. The best way to do this is to dampen a cotton swab in distilled water and using it to absorb the stain. The stain is then allowed to air dry before packaging. It is important to note that these DNA samples quickly decompose.

This reason makes plastic bags unsuitable for storage as they catalyze the decomposition. Instead, a paper envelope is encouraged for the collection of the evidence sample as it allows for the aeration and maintains a pure and uncontaminated sample (Spear, n.d.).

Human blood is the first sample that is important in determining the identity of the involved parties in a crime scene. The blood consists of erythrocytes, leukocytes, and platelets. The blood is taken through several procedures to establish the DNA make-up of the blood that was collected. The cells collected are and the cell membrane broken by using detergents and surfactants. The protease and RNase break down the proteins and the RNA, respectively. Treatment with a saline solution allows the debris to clump together and the solution further exposed to a centrifugal force to separate it from the solution. The DNA is then purified from the detergents, surfactants, and other chemicals used in the previous process. The DNA is isolated from the bounded proteins. The DNA dethawed in a somewhat basic buffer (Weedn, Rogers, & Henry, 1998).

Semen, on the other hand, involves prior methods which detect the presence of sperm in the collected samples. These tests also play an essential role in determining the nature of the sexual activity involved during the crime. Due to the dilution and commingling of the semen with other body fluids, the techniques employed should be of high sensitivity and specificity. The collected sample is, therefore, deposited in aliquots and dried on a cotton-polyester cloth at room temperature for about forty-eight hours. After this, the DNA gets extracted and the materials used to begin the quantitation. The DNA is amplified over and over until it reached full volume and 0.5-ng template added ().

As for the saliva, the primary test for presence is the detection of the amylase enzyme. This enzyme is present in saliva and is usually responsible for the kicking-off of digestion in the mouth. Saliva is also a critical element in forensic investigations. The sample is placed in a petri dish and allowed to diffuse through the night. Iodine addition as a stain on the saliva follows. Presence of the spit confirms by the formation of bright colour encircling the sample. The saliva test has, however, not been brought to advancement as much as the blood and semen samples.

From all the collected samples, the results portray a similarity in a diversified manner. For instance, the mentioned body fluids can emit a glow when exposed to light rays with auto-fluorescence. The Phadebas test is an excellent example of a test that is known to portray the similarity between different body fluids. Amylase, which is the enzyme tested by the test, is present in most of the body fluids. The possible test used to detect seminal acid phosphatase is also limited to the same case. On top of this, the criteria used in the identification of all these body fluids often provide false results. The reason behind this is the lack of uniqueness of the substances tested not only in other human fluids but even other animals as well.

All the same, these body fluids are also unique in their ways. This fact lays a foundation for the ability to deduct the sample to be a given fluid specifically. A good example is how the different fluids glow in fluorescent lights. Saliva is known to shine at a more moderate degree when compared to the other fluids. These little tiny details allow the laboratory personnel to proceed to carry out additional tests with hope of determining the available fluid. The test for blood involves a process that breaks down the cell membranes and centrifuging the DNA to attain a sample that can then tie the suspected victim to a crime.

Although the tests prove to be quite diverse in showcasing the desired results, the fact remains unchanged. The perfect delivery of results from collected samples is out of question, but the availability of a suspect simplifies this matter. Samples from the crime scene get compared to the ones from the suspected individual. A match of the two DNA make-up leads to an inevitable entanglement of the suspect to the stage. Otherwise, the suspect is assumed free and uninvolved.

Reference

Budowle, B., Schutzer, S. E., Burans, J. P., Beecher, D. J., Cebula, T. A, Chakraborty, R., … & Heitkamp, M. A. (2006). Quality sample collection, handling, and preservation for an effective microbial forensics program.

Peterson, J., Sommers, I., Baskin, C, & Johnson, C. (2010). The role and impact of forensic evidence in the criminal justice process. National Institute of Justice (2010): 1-151.

Procedures for Evidence Collection, Handling, and Storage. (2019). Retrieved from https://www.fws.gov/policy/e1445fw3.html

Spear, T. F. (n.d.). Sample Handling Considerations for Biological Evidence and DNA Extracts. Retrieved from https://www.crime-scene-investigator.net/sample-handling-considerations-for-biological-evidence-and-DNA-extracts.html

Weedn, V. W., Rogers, G. S., & Henry, B. E. (1998). DNA testing in the forensic laboratory. Laboratory Medicine, 29(8), 484-489.

Rodriguez, J. J. R. B., Calacal, G. C., Laude, R. P., & De Ungria, M. C. A. (2019). Integrating presumptive and confirmatory semen tests into DNA profiling of sexual assault evidence: a Philippine example. Egyptian Journal of Forensic Sciences, 9(1), 45.