Presentation on theme: "BLOODSTAIN PATTERNS. Interpretation of Bloodstains The location, distribution, and appearance of bloodstains and spatters are useful for reconstructing."— Presentation transcript:
Interpretation of Bloodstains The location, distribution, and appearance of bloodstains and spatters are useful for reconstructing and interpreting the events that produced bleeding
Surface texture Correlations between standards and unknown samples are valid only if identical surfaces are used The harder and less porous the surface, the less spatter
Direction of Travel Pointed end of bloodstain always faces the direction of travel
Angle of impact on a flat surface Angle of impact is obtained by measuring the degree of circular distortion
Origin of Blood spatter Draw straight lines through the long axis of several blood stains – area of convergence is origin of blood
Know the difference between spatter, transfer, and swipe The following Information may be obtained from a proper Bloodstain Pattern Analysis: 1. Distance from the blood source to the target 2. Direction of travel and impact angles 3. Nature of the force used to cause the bloodshed 4. The object used to cause the bloodshed 5. Sequencing of multiple bloodshed events 6. Interpretation of contact or transfer patterns
SPATTER VS TRANSFER The simplest type of blood spatter analysis is determining spatters from transfers Spatters are created when blood is acted upon by force, and travels through the air before landing on a target surface Transfers occur when a blood source comes in direct contact with a target surface area.
Textbook page 283 Example of crime scene reconstruction using blood spatter formations shown figures 8-12 – 8-14 This robbery/homicide case relates to an elderly male found dead on his living room floor He had been beaten about the head and face, then stabbed in the chest
Reconstruction of bloodstains found on the interior front door and adjacent wall documented that the victim was beaten about the face with a fist and struck on the back of his head with his cane When suspect was apprehended, he had an acute fracture of the right hand
PRINCIPLES OF HEREDITY
Locus Allele Genotype Phenotype Position of gene on chromosome One of a gene pair Gene pair Physical trait
Paternity testing Many cases of disputed paternity can be resolved by comparing the blood group genotypes of the suspected parents and the offspring The more blood group factors compared the more certainty can be attained
Forensic Characterization of Semen Two step process Locate the semen stain Outer garments, undergarments, bedclothes Subject the stain to testing Identity of male depositor Blood type of male depositor
Testing for Seminal Stains Acid Phosphatase test Microscopic examination of semen PSA (prostate specific antigen) Also can test sperm for DNA typing
Acid Phosphatase Test Presence of semen Sodium alpha naphthylphosphate and Fast Blue B dye will turn acid phosphatase purple 4-methyl umbelliferyl phosphate (MUP) will cause acid phosphatase to fluoresce
Microscopic Examination of Semen Presence of spermatoza – usual amount in ejaculation is million Oligospermia Aspermia
Prostate Specific Antigen Can test suspected semen stains that have no sperm P30 (PSA) is unique to seminal plasma Produces polyclonal antibodies Two means of testing
PSA Testing by Electrophoresis
Ab-Ag-Ab complex is 100 times more sensitive than PSA electrophoresis
Collection of Rape Evidence Rape victim must undergo medical examination ASAP after the assault Clothing, hairs, and vaginal and rectal swabs collected for lab examination
Facts and Concepts Why must a rape victim stand on a sheet of paper while disrobing for forensic analysis? A rape victim must stand on a new, clean sheet of paper (not contaminated) so that the investigator can collect any loose foreign material that falls from the victim or the clothing onto the paper.
Besides swabbing for semen constituents, what other bodily fluids should be collected from a rape victim during a medical exam? Other than oral, vaginal, cervical, and rectal swabs, blood and urine samples should be collected from a rape victim during a medical exam
What items should be collected from the suspected perp of a sexual assault? All clothing and any other items worn during the time of the assault Pubic hair combings Pulled or cut head and pubic hair standard/reference samples
Penile swabs – when appropriate to case history Blood sample or buccal swab for DNA typing
How long do motile sperm generally survive in the vaginal cavity of a living female? Motile (living and moving) sperm generally can survive for 4 – 6 hours in the vaginal cavity of a living female.
How long do nonmotile sperm generally survive in the vaginal cavity of a living female? Nonmotile (nonliving) sperm may be found in a living female for up to three days after intercourse and occasionally up to six days.