H - Blood Spatter Analysis

Blood Spatter Analysis

CSI

History 1894 - Pitorowski wrote earliest reference to

bloodstain pattern analysis 1939 - Balthazard was first to use physical

interpretations of stains 1955 - Dr. Paul Kirk used bloodstain pattern

interpretation as a defense witness in the Sam Shepherd case

1971 - Professor Herbert MacDonnell promoted bloodstain pattern interpretation as a tool for modern criminalistics

1983 – The International Association of Bloodstain Pattern Analysis was formed

Blood Basics

Red Blood Cells(Erythrocytes)-most abundant, contains a liquid called plasma, carries oxygen.

White Blood Cells(Leukocytes)-Part of immune system.

Platelets-In charge of the clotting factor.

Classification

ABO-Basic classification for blood types

A,B,AB,O-Blood types AB-universal receiver O-Universal Donor RH+-has d antigen RH—has no d antigen

Human or Animal?

Precipitin Test PT- animal serum contains antibodies

specific to human antigens, therefore it reacts to agglutinate human blood.

Detection of Blood

CSI can use the location, distribution and pattern of blood and bloodstains to reconstruct the crime.

Investigators can individualize blood evidence by comparing DNA.

Several methods such as luminol can be used to detect blood by reacting certain chemicals with the iron in the hemoglobin and making it glow blue.

Blood Pattern Analysis

The use of physics and math to interpret bloodstain patterns within a forensic setting

Blood Spatter patterns are often used to prove or disprove the suspect’s account of what happened.

May show:1. Activity at scene2. Number of blows3. Position of victim and assailant4. Whether death was immediate or

delayed5. Weapon characteristics

Basic principles

A free falling drop of blood forms a sphere or ball.

A spherical drop will break1. When it strikes another object2. When acted upon by some force

Blood Spatter Analysis

Blood spatter is determined by distance, velocity, angle of impact, direction of travel and position of origin

Spatter size is dependent upon velocity

Low velocity spatter is about 5 ft / second and usually 3 mm or greater in diameter and indicates blood is dripping

Medium velocity spatter is 5 – 25 ft / second with a <3 mm diameter and usually indicates blunt trauma or sharp trauma or it could be cast-off

High velocity spatter is 100+ ft / second with a spatter of < 1 mm indicating gunshot trauma, power tools, an object striking with extreme velocity (airplane prop) or an explosion, may be referred to as fly specks

Determining Location of Blood Source

Direction of travel – tail will point in direction of travel

Angle of impact 1. Vertical drops are circular2. Drop elongates as angle increases

Measure width and length then calculate angle it struck the surface

Attach string lines to each of the spatters and lines converge at the blood source

Angle of Impact“The tail tells the tale”

90 degrees –

60 degrees –

30 degrees –

10 degrees –

String Convergence in a 2 Dimensional Plane

Convergence

Cast-off Bloodstains

Arterial Gushing

Other Patterns in Blood

Transfer patterns (gun, knife, hand, foot…)

Void patterns (indicating some object was removed or a person was hit by spatter)

Flow patterns (may indicate movement with change in flow)

Drying Time

Drying begins at periphery and proceeds inward

Drying time is affected by – Surface type– Amount of blood– Climatic conditions

Skeletonization– Partially dry stains leave a ring that outlines

original spatter– The drier the stain, the less skeletonization

shown

Quiz Questions

1. Red blood cells are also known as _______. 2. Another name for white blood cells is _______.3. What is the name of the test used to determine whether the

blood sample is human or animal? 4. Blood patterns in a crime scene may showA. Race of suspectB. Age of the victimC. How many children they hadD. Position of victim and assailant

5. True or False : Spatter size is dependent upon velocity.

Answers

1. Erythrocytes 2. Leukocytes 3. Precipitin Test 4. D 5. True