2 ObjectivesList the laboratory tests necessary to characterize seminal stainsExplain how suspect blood and semen stains are properly preserved for laboratory examinationDescribe the proper collection of physical evidence in a rape investigation.
3 Characterization of Semen Normal male releases 2.5 to 6-mL during ejaculationEach mililiter contains 100 million+ spermatozoaSperm are indicative of semenOligospermia – low sperm countAspermia – no sperm in seminal fluid
4 Forensic examination for seminal stain 2 step processStain must be located usually using an acid phosphatase color testAcid phosphatase = enzyme secreted by the prostate gland into seminal fluidConcentrations are up to 400x greater than in other bodily fluidTurns purple when reacted with acidic solutionsFluoresces under UV light with 4-methyl umbelliferyl phosphate (MUP)Subject to test to prove its identity
5 SemenProtein p30 or prostate specific antigen (PSA) is a protein unique to seminal plasmaStimulates the production of polyclonals when injected into a rabbitCurrently a new technique is used that places a monoclonal PSA antibody on a porous membrane which then moves toward a polyclonal PSA also on the same membrane
6 Rape EvidenceSeminal constituents on a rape victim are important evidence that sexual intercourse took placeTheir absence does not necessarily mean that a rape did not occurPhysical injuries such as bruises and bleeding tend to confirm that a violent assault occurredForceful physical contact between victim and assailant may results in the transfer of physical evidence – blood, semen, hairs, fibers
7 Collection of Rape Evidence To protect the evidence, all outer garments and undergarments of the persons involved are carefully removed and packaged separately in paper bagsA clean bed sheet and clean paper sheet are placed on the floor and the victim removes all their clothingPaper collects any loose foreign material falling from the clothingEach piece of clothing is individually bagged to avoid cross-contaminationPaper is carefully folded to keep all foreign material inside
8 Collection of Rape Evidence CONT…. Items suspected of containing seminal stains are carefully handledFolding the article can cause the stain to flake offRubbing against the surface of the packaging material can also cause flakingAnalysts try to link seminal material to donor(s) using DNA typingIndividuals may transfer their DNA types to a stain through perspiration, so special care must be taken to minimize direct personal contact with the stain
9 Collection of Rape Evidence CONT…. Rape victim undergoes a complete medical examination as soon as possible following the assaultPhysical evidence is collected by trained personnelIt includes: pubic combings, pubic hair standard/reference sample, external and internal genital skin area swabs (vaginal, cervical, rectal, oral), head hairs, blood sample, fingernail scrapings, all clothing, urine specimen.
10 Collection of Rape Evidence CONT…. From the suspect, physical evidence is also collected.It includes: all clothing, pubic hair combs, pulled head and pubic hair standard/reference samples, penile swab, and blood sample or buccal swab for DNA
11 12.6 QuestionsWhat test is used to locate and characterize seminal tissue? Why is it useful?Differentiate between oligospermia and aspermiaWhat protein is indicative of semen and what two tests are used to detect this protein?Why must a rape victim stand on a sheet of paper while disrobing for forensics analysis?Besides swabbing for semen constituents, what other bodily fluids should be collected from a rape victim during a medical examination?What items should be collected from the suspected perpetrator of sexual assault? (at least 4 things)How long do motile sperm generally survive in the vaginal cavity of a living female?How long do non-motile sperm generally survive in the vaginal cavity of a living female?