Blood PatternsForensic Science

A Brief Intro to Blood Spatter Analysis

• Blood contains DNA, so it is possible to identify its exact source.

• The shape of the spatter indicates:1. the point of origin2. direction of travel, and 3. angle of impact.• Certain chemicals can detect the

presence of blood even when it is not visible

BLOOD TYPES

• Four types of blood- A, B, AB, O

Type A contains the A proteinsType B contains the B proteinsType AB contains both A & B proteinsType O contains neither A nor B

proteins

The Rh Factor

• This is the + or – after the blood type

A+, A-, O+, O-…and so on.

+ means the Rh protein is present, - means the Rh protein is absent

BLOOD COMPATIBILITY

• Type O- is the universal donor- all other blood types can accept type O blood

• Type AB+ is the universal recipient- it can take all other types of blood

MORE ON COMPATIBILITY

Type O+: takes O- or O+Type O-: takes O-Type A+: takes A+, A-, O+ or O-Type A-: takes A- or O-Type B+: takes B+, B-, O+ or O-Type B-: takes B- or O-Type AB+: takes A+, A-, B+, B-, AB+, AB-, O+,

O-Type AB-: takes A-, B-, AB-, O-

Basic Info on Shapes of Drops

• The “tail” points in the direction of travel.

• Drop at 90 degree angle will be circular.

• Drop at less than 90 degree angle will be elliptical

PRESERVING BLOOD EVIDENCE

• Never place bloody evidence in plastic…it could promote mold growth and destroy the sample.

• Blood soaked evidence should be placed in paper.

NEXT: EXAMPLES OF BLOOD SPATTERS

Arterial Blood

Cast Off

Drip

Flow Pattern

Hair Pattern

Low Velocity

Medium Velocity

High Velocity

Swipe Pattern

Transfer from Hammer

Transfer from Screwdriver

Transfer from Fingers

Transfer from Footwear

Transfer from Knife Blade

Wipe from Drying Blood Drop

The End

References:Forensic Science: An Introduction to

Scientific and Investigative Techniques by Stuart H. James & Jon J. Nordby

Images from www.peelpolice.on.ca