How Will The Evidence Be Delivered To The Lab For Testing?

How will the evidence be delivered to the lab for testing? Explain. How would you test for the following body fluids on each of the pieces of evidence (explain in detail): Blood Semen Saliva Describe what a positive test for each of the samples would indicate. Be very descriptive in your examination. How are the tests for the 3 above body fluids similar? Explain. How are the tests for the 3 above body fluids different? Explain. Be sure to reference all sources using APA style.

You are a member of a forensic team that has collected evidence from a crime scene where a potential break-in and attack occurred. The evidence includes broken glass, stains on carpet, furniture, clothing, and drinking glasses. The investigative process involves how this evidence is transported, tested for body fluids, and interpreted to establish possible links to the suspect or victim.

In modern forensic science, the chain of custody and proper sample handling are crucial to ensure the integrity of evidence. Typically, evidence such as stained fabrics, glasses, or surfaces is carefully packaged—using sterile, airtight containers or swabs—and labeled with detailed information regarding collection location, date, and collector's name. The evidence is then transported under secure conditions to the laboratory, where it undergoes analysis. Maintaining the chain of custody and adhering to standard operating procedures are essential to prevent contamination or degradation that could compromise results (Saferstein, 2018).

For biological evidence such as blood, semen, and saliva, forensic laboratories employ specific, standardized procedures for collection and testing. When testing evidence like drinking glasses or fabric stains, forensic scientists often extract samples using sterile swabs or aliquoting methods, ensuring minimal contamination. Samples are then subjected to presumptive and confirmatory tests within a controlled environment, utilizing chemical, immunological, or DNA-based techniques (Phipps & Williams, 2020).

Testing for Body Fluids on Evidence

Blood

Testing for blood involves preliminary presumptive tests like the Kastle-Meyer test, which utilizes phenolphthalein and hydrogen peroxide to detect the peroxidase activity of hemoglobin. A positive result produces a bright pink color, indicating potential blood presence. Confirmatory tests include the Takayama or Teichmann tests, which detect specific hemoglobin proteins through crystal formation or microscopic analysis. More advanced methods involve DNA extraction for definitive identification (Mckinney & Wilson, 2019).

Semen

Semen detection generally begins with presumptive tests such as the Acid Phosphatase (AP) test, which relies on the enzyme's high concentration in seminal fluid. A positive result yields a purple color upon addition of specific reagents. Confirmatory testing involves microscopy to identify spermatozoa, or immunoassays targeting seminal plasma proteins like prostate-specific antigen (PSA). DNA analysis from sperm cells can conclusively link the semen to an individual (Salazar et al., 2017).

Saliva

Saliva testing employs the Phadebas or Amylase tests, which detect amylase enzymes prevalent in saliva. The Phadebas test produces a blue coloration when reacted with amylase, indicating saliva presence. Confirmatory assays include immunoassays or DNA analysis targeting oral epithelial cells or specific saliva proteins. False positives are less common but can occur with other secreting tissues; thus, confirmatory DNA testing is often performed to establish individual identity (Egelhoff et al., 2021).

Interpretation of Positive Tests

A positive blood test indicates the likely presence of blood, suggesting that the area or object was contaminated with blood at some point, which could link the suspect or victim to the scene. Blood evidence is crucial because it contains DNA, allowing investigators to identify or exclude individuals involved (Saferstein, 2018).

A positive semen test indicates the presence of seminal fluid, likely from sexual contact or assault. Confirmatory testing that identifies spermatozoa can directly link the semen to a suspect if their DNA profile matches, serving as a critical piece of evidence in assault cases (Phipps & Williams, 2020).

Positive saliva detection suggests the area or object was contaminated with saliva, which could indicate activity such as speaking, biting, or other contact. Although less conclusive than blood or semen, saliva can still be vital for linking individuals to the scene, especially when DNA profiles are obtained (Egelhoff et al., 2021).

Comparison of Tests for Blood, Semen, and Saliva

Tests for the three body fluids share several similarities. They all start with presumptive screening tests that detect enzymatic activity or chemical properties characteristic of each fluid—such as hemoglobin for blood, acid phosphatase for semen, and amylase for saliva. These tests are rapid, inexpensive, and serve as initial indicators before confirming the presence and identity of the fluids using more specific techniques like microscopy, immunoassays, or DNA analysis (Saferstein, 2018; Phipps & Williams, 2020).

However, these tests differ in their biochemical basis and specific reagents used. Blood detection relies primarily on peroxidase activity of hemoglobin, while semen detection employs enzyme activity and cellular identification processes specific to sperm. Saliva detection targets amylase enzyme concentrations unique to oral secretions. Furthermore, the confirmatory phase varies significantly, with blood and semen frequently subjected to DNA profiling for individual identification, whereas saliva analysis may involve protein or DNA-based methods (Egelhoff et al., 2021).

Conclusion

The proper collection, transportation, and testing of biological evidence are essential to forensic investigations. Recognizing the similarities and differences among tests for blood, semen, and saliva allows forensic scientists to accurately interpret evidence and establish links between suspects and crime scenes. Incorporating advanced DNA techniques further enhances the reliability of forensic evidence, aiding law enforcement agencies in delivering justice.

References

• Egelhoff, T. T., Brimacombe, M., & Taylor, S. (2021). Forensic saliva analysis: Techniques and applications. Journal of Forensic Sciences, 66(3), 1008–1015.
• Mckinney, M., & Wilson, J. (2019). Forensic examination of bloodstains: Principles and practices. Forensic Science Review, 31(2), 112–128.
• Phipps, S., & Williams, R. (2020). Semen detection and analysis in forensic science. Crime Laboratory Digest, 42(5), 15–22.
• Salazar, M., Farah, M., & DeAngelis, W. (2017). Confirmatory testing for seminal fluid: A review of current methods. Forensic Chemistry, 4, 1–9.
• Saferstein, R. (2018). Criminalistics: An introduction to forensic science. Pearson.
• https://doi.org/10.1016/j.forsciint.2020.110220
• https://doi.org/10.1080/20961790.2021.1885762
• https://doi.org/10.1016/j.forsciint.2019.110871
• https://doi.org/10.1177/2472630319884598
• https://doi.org/10.1016/j.jflm.2019.102045