Forensic Serology

Forensic Serology

Forensic Serology BLOOD SPATTER Blood drips from injuries sustained during an International Fighting League match in New Jersey High-velocity spatter and blood drips after a suicide bombing in Dimona, Israel Categories of Blood Stains Passive

Transfer Projected Transfer Bloodstains A transfer bloodstain is created when a wet, bloody surface comes in contact with a secondary surface. A recognizable image of all or a portion of the original surface may be observed in

the pattern, as in the case of a bloody hand or footwear. Passive Bloodstains Passive bloodstains are drops created or formed by the force of gravity acting alone. PASSIVE DROPS

Spilled Blood Dripped Blood Projected Bloodstains Projected bloodstains are created when an exposed blood source is subjected to an action or force, greater than the force of gravity. (Internally or Externally

produced) The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source. Projected Bloodstains Arterial Spurt/Gush

Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery Cast-off Stains Blood released or thrown from a blood-bearing object in motion

Impact Spatter Blood stain patterns created when a blood source receives a blow or force resulting in the random dispersion of smaller drops of blood. Velocity affects stain pattern Impacted Spatter

Medium Velocity Low Velocity High Velocity Directionality of Bloodstains When a droplet of blood strikes a surface perpendicular (90 degrees) the resulting bloodstain will be circular. That being the length and width of the stain will be equal.

Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape. Directionality is usually obvious as the pointed end of the bloodstain ( tail ) will always point in the direction of travel. Angle of Impact

angle of impact = arcsin (opposite side/hypotenuse) Here's what an analyst has to do to for this to work: Measure the length and width of the splatter. Divide the width of the splatter by its length. Determine the arcsin of that number, typically using a

calculator with an arcsin function. Angle of Impact A drop of blood that fell perfectly vertically, or at a 90-degree angle, will be round. As the angle of impact increases, the drop of blood gets longer and develops a "tail." This tail points in the direction

that the drop traveled, but its length isn't part of the measurements. Convergence Illustration of stain convergence on a threedimensional plane. Convergence represents the

point from which the stains emanated. Testing for Seminal Stains Many of the cases sent to a forensic laboratory involve sexual offenses, making it necessary to examine exhibits for the presence of seminal stains. The best way to locate and at the same time characterize a seminal stain is to perform the acid phosphatase (an enzyme secreted into seminal fluid)

color test. A purple color indicates acid phosphatase enzyme. A screening test for semen by determining acid phosphatase content; because seminal fluid contains high concentrations of acid phosphatase, while other body fluids and extraneous foreign materials have very low concentrations, high values of acid phosphatase on vaginal aspirate or lavage, or on wash fluid from stains, render positive identification of semen, even if the male is aspermic. Testing for seminal stains Semen can be unequivocally identified by

either the presence of spermatozoa or of p30, a protein unique to seminal plasma. Forensic scientists can successfully link seminal material to an individual by DNA typing. Rape Evidence The rape victim must undergo a medical examination as soon as possible after the assault. At that time the appropriate items of physical evidence including clothing, hairs, and vaginal and rectal swabs can be collected for subsequent

laboratory examination. All outer and undergarments should be carefully removed and packaged separately in paper (not plastic) bags. Bedding, or the object upon which the assault took place, may also be carefully collected. Physical Evidence from the Victim Pubic combings Pubic hair standard/reference sample

External genital dry-skin areas Vaginal swabs and smear Cervix swab Rectal swabs and smear

Oral swabs & smear Head hairs Blood sample Fingernail scrapings All clothing Urine specimen Rape Evidence If a suspect is apprehended within 24 hours of the assault, it may be possible to detect the victims

DNA on the males underwear or on a penile swab of the suspect. Items routinely collected from the suspect include all clothing, pubic hair, head hair, penile swab, and a blood sample or buccal swab for DNA typing. The forceful physical contact between victim and assailant may result in a transfer of such physical evidence of blood, semen, saliva, hairs, and fibers.

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