Serology - Forensic Science - Lecture Slides, Slides of Forensics

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Serology

Ch. 12

Blood Stain Characterization

 Three Questions:

 Is it blood?

 If it is blood, which species did it come from?

 If it is human blood, can we isolate a single

individual?

Is it human blood?

 Precipitin test

 Antiserums have been designed for most

species of animals. If the blood is human then it

should react with human antiserum.

 The test is very sensitive and requires only a

minute amount of blood. Positive tests have

resulted for samples 10-15 years old and tissue

sample from mummies that are thousands of

years old.

Whose blood is it?

 Before 1995, we could only identify a source

down to a particular blood group (ABO +

enzymes).

 One particular enzyme studied was PGM which

exists in different forms

 Since the onset of DNA testing, blood typing

has become all but obsolete.

Bloodstain Pattern Analysis Terms

 Spatter – Bloodstains created from the application of force to the area

where the blood originated.

 Origin/Source – The place from where the blood spatter came from or

originated.

 Angle of Impact – The angle at which a blood droplet strikes a surface.

Parent Drop

Spines

Satellite Spatters

• Parent Drop – The droplet from which a

satellite spatter originates.

• Satellite Spatters – Small drops of blood

that break of from the parent spatter when

the blood droplet hits a surface.

• Spines – The pointed edges of a stain that

radiate out from the spatter; can help

determine the direction from which the

blood traveled.

Spatter Analysis

 Surface texture is extremely important in spatter

analysis. The harder and less porous the surface,

the less spatter.

Direction of Travel

 The pointed end of the spatter indicates the

direction of travel.

Point of Origin

 Point of origin can be

established by drawing

straight lines through the

long axis of blood stains

and finding the point of

convergence.

 Passive Bloodstains

 Patterns created from the force of gravity  Drop, series of drops, flow patterns, blood pools , etc.

• Projected Bloodstains
  • Patterns that occur when a force is applied to the source of the blood
  • Includes low, medium, or high impact spatters, cast- off, arterial spurting, expiratory blood blown out of the nose, mouth, or wound.
• Transfer or Contact Bloodstains
• These patterns are created when a wet, bloody object comes in contact with a target surface; may be used to identify an object or body part.
• A wipe pattern is created from an object moving through a bloodstain, while a swipe pattern is created from an object leaving a bloodstain. Images from http://www.bloodspatter.com/BPATutorial.htm

Types of Bloodstain Patterns

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Testing for Semen

 Acid Phosphatase Color Test

 Acid phosphatase is an enzyme secreted by the

prostate gland that is released into semen. By

adding a sodium alpha naphthylphosphate and

Fast Blue B dye. This test is done on filter paper

and gives a purple color

 MUP

 Causes semen to glow in UV light. A reaction in

less than 30 seconds is a positive result.

Testing for Semen

 Presence of sperm

 Oligospermia—low sperm count

 Aspermia-lack of sperm (usually the result of a

vasectomy)

 PSA (prostate specific antigen) chemical

that definitively proofs that a sample is

semen.