Bloodstain Pattern Analysis

Bloodstain Pattern Analysis

Study of bloodstains in a crime scene or on physical evidence to determine the mechanism that caused them

Post-Incident Artifacts

Changes in bloodstain patterns based on events that occurred after the initial incident that caused the stain

What MAY BPA assist with?

• location and description of individual stains and patterns

• Mechanism that created the stains (type of object and number of blows)

• Presence or absence of a subject; positioning of victim, suspect, or objects

• Refute or corroborate statements

• Reconstruction of events

• Exoneration of the innocent

What CAN BPA determine?

• Location and description of individual stains and patterns

• Direction a blood droplet was traveling

• Movement of a victim during and after the event

• Presence or absence of a subject at a scene

  • Positioning of the victim, suspect, and objects during events

• Refute or corroborate witness, suspect, and victim statements

• Sequence of events

• Which stains should be analyzed

Blood

Connective tissue that consists of plasma (55%) and formed elements (45%)

Plasma

Clear extracellular fluid

Formed Elements

Erythrocytes, leukocytes (WBCs) and platelets

How much of our total body weight is contributed by blood?

8% of our body weight

What allows for the accurate analysis of bloodstains?

• Well defined constituents of blood

• Blood behaves in a predictable manner due to its:

  • viscosity

  • surface tension

  • specific gravity

Separation and clotting

Occurs a while after the initial event; Head wounds: contain an extra enzyme that speeds this up (saliva and spinal fluid also)

What scientific fields does BPA apply scientific knowledge from?

• Biology

• Physiology

• Anatomy

• Chemistry

• Fluid dynamics

• Math

• Physics

Utilizes these fields to solve practical problems

What are the keys to success in BPA?

• Use SOLID scientific method

• NEVER speculate or assume

• Examine all possible explanations

• Know your own own limitations

• Be able to say “I do not know”

• Base all assumptions on fact

• ASK FOR ASSISTANCE

1895 - Dr. Eduard Piotrowski

First published reference to BPA; Determined several key features of blood behavior

1955 - Dr. Paul Leland Kirk

Was one of the first times BPA was used in an investigation; Murder of Marilyn Sheppard

1971 - Herb MacDonell

Considered the “Father of BPA”; Published the “Flight Characteristics and Stain Patterns of Human Blood” and also conducted the first BPA training course (in 1983 his students created the IABPA)

How do we know the stain is blood?

Needs to be tested before BPA is performed (ex. phenolphthalein, blue star, etc.)

What are the bloodstain pattern categories?

• Passive bloodstains

• Projected bloodstains

• Transfer bloodstains

Passive Bloodstains

Force acting on the blood to create the pattern is gravity

What types of blood stains are under the passive bloodstain category?

• Passive drop

• Flow patterns

• Drip patterns

• Drip trails

Passive Drop

Typically circular stain, can be different based on the surface, that is created when blood falls with no outside force or movement

Flow Patterns

Drip-like produced when blood flows down a surface due to gravity or the movement of the target

Drip Patterns

Pattern that occurs when a liquid, sometimes blood, drips into another liquid, also sometimes blood

Drip Trail

Pattern that is produced from a moving source of drip stains between two points (indicates movement)

Projected Bloodstains

A form of energy has been transferred to the blood source to cause the pattern

What types of blood stains are under the projected bloodstain category?

• Arterial spurting or gushing

• Cast off

• Radiating spatter

  • Impact

  • Backspatter and foreward spatter

Arterial Spurting or Gushing

Pattern produced by a ruptured artery or heart; The blood is forced out of the body in a rapid, intermittent spray through the power of the cardiovascular system (large amount of blood)

Cast Off

Pattern that results from blood droplets being released from a moving object (like a weapon); The droplets are linear and follow the trajectory of the movement

Impact Spatter

Pattern produced when an object hits a blood source (the angle of object impacts blood pattern)

Backspatter

Pattern that occurs when blood is projected in the opposite direction of the force applied (ex. may be seen on hands after firing a gun)

Foreward Spatter

Pattern that is produced when blood droplets travel in the same direction as the force of impact

Transfer Bloodstains

An object with blood comes into contact with an object or surface without blood

What types of blood stains are under the transfer bloodstain category?

• Swipe pattern

• Wipe pattern

• transfer pattern

Swipe Pattern

Blood on an object or person comes into contact with something (with movement) that does not have blood on it already

Wipe Pattern

Blood was deposited and started drying before a clean object was moved across it (usually from cleaning); This causes the blood to be moved, removed, or altered

Transfer Pattern

Shows detail of object with blood on it

Area of Convergence

Area where event occurred that is extrapolated from the directionality of bloodstains

How does the texture/type of surface the blood is deposited on affect the resulting bloodstain pattern?

It affects the amount of resulting spatter and the size and appearance of blood drops

What is the methodology of BPA?

1. Documentation of stains

2. Classification of patterns

3. Analyzing patterns in broader context of the scene

4. Peer review of conclusions

What is the most important step of BPA?

Documentation!!

Roadmapping

• Created by Toby Wolson in 1994

• Uses ‘road signs’ for the analyst to follow

• Last step of the documentation process because it causes alterations to the scene

• Breaks down the scene into smaller chunks

  • in each chunk: the size, shape, distribution, and location is looked at broadly first

    • What are you looking at?

    • Basic descriptions using appropriate terminology