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IDENTIFICATION OF BIOLOGICAL FLUIDS AND STAINS

IDENTIFICATION OF BIOLOGICAL FLUIDS AND STAINS. ID OF SEMEN. Why is semen important in an investigation? Evidence in sexual assault cases Can prove crime was committed Can identify perpetrator. SEMEN. What is semen?

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IDENTIFICATION OF BIOLOGICAL FLUIDS AND STAINS

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  1. IDENTIFICATION OF BIOLOGICAL FLUIDS AND STAINS

  2. ID OF SEMEN Why is semen important in an investigation? • Evidence in sexual assault cases • Can prove crime was committed • Can identify perpetrator

  3. SEMEN What is semen? • cells, amino acids, sugars, salts, ions and other organic and inorganic material

  4. SPERM CELL Also called spermatozoan Approx 55 μm in length Head contains cell nucleus which packed with DNA

  5. SEMEN IDENTIFICATION Presumptive test • Test for SAP (seminal acid phosphatase) • Look for color change • BrentamineFast Blue Test • get intense purple color within 2 minutes

  6. CONFIRMATORY TEST Microscopic examination Motility usually not apparent by time lab gets stain Use staining techniques

  7. CONFIRMATORY TEST • Commonly used staining techniques • Picroindigocarmine (PIC) • Nuclear Fast Red (aka Christmas tree stain)

  8. PREPARATION STAINING Need to determine best use of sample Only single intact sperm cell needed to ID sperm however, 80 sperm cells required for DNA profile

  9. What determines if semen will be found Time since intercourse If clothing has been washed SAP is water soluble SAP can be detected after dry cleaning

  10. Exam Strategy Sexual assault kits utilized to collect evidence – “rape kits” Swabs examined first Liquid samples examined next

  11. SALIVA Contains water, mucus, proteins, salts and enzymes Human produce 1-1.5 liters per day

  12. METHODS FOR ID OF SALIVA No test specific for saliva Basically looking at amylase Problems with amylase, also found: Pancreas, perspiration, vaginal secretions, and semen

  13. IDENTIFICATION OF URINE Searching for Urine Cases of harassment, mischief, sexual assault, etc. Stains identified through visual examination (alternate light may help) Rarely used; difficult to identify as urine and difficult to get DNA profile

  14. IDENTIFICATION OF FECES • Undigested food, mucosal cells, bacteria • Identified by greenish brown color, odor, undigested food Feces end product after digestion

  15. IDENTIFICATION OF FECES DNA testing of Feces Low cell count and high bacteria content make testing difficult, but not impossible

  16. FECES DNA testing unsuccessful due to inhibitory effects of bile pigments

  17. IDENTIFICATION OF VOMITUS • Possibly look at low pH, or undigested food No known test

  18. CASE EXAMINATION STRATEGY Determine if body fluid is present Record findings Determine necessity of further testing Determine type of further testing

  19. ALWAYS NEED TO CONSIDER Assess type and whether victim alive Awareness of victim Number of people involved Relationship of principals Time elapsed Actions after event

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