Bloodstain Pattern Analysis

Summary

What is Blood? Determining Distance of Blood Determining Direction of Blood Types of Blood Stain Patterns

What is Blood?

Introduction to Blood

Blood Spatter (or splatter)

Blood drops form different shapes and sizes

Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

Determining Distance Blood Falls

Blood drops fall as small spheres

Blood Spatter > Distance

Determining Distance Blood Falls

Drops form circle when hitting surface Size depends on speed of blood drop

Blood Spatter > Distance

Determining Distance Blood Falls

Faster drop = larger diameter (size)

Higher distance = larger diameter

Due to air resistance, speed maxes out at distances above about 7 feet

Blood Spatter > Distance

Determining Distance Blood Falls

However, size of drop also depends on the volume of the drop.

Volume depends on the object blood originated from (needle = small; bat = large).

Blood Spatter > Distance

Determining Distance Blood Falls

Since the volume of blood is unknown…

The distance a drop has fallen cannot be measured.

Blood Spatter > Distance

Effect of Surface

Smooth surface = smooth sphere Rough surface may cause some splatter

Blood Spatter

Determining Direction of Blood

Narrow end of a blood drop will point in the direction of travel.

Blood Spatter > Direction

Determining Direction of Blood

If more than one drop (from spatter) results, the point of origin can be determined

Blood Spatter > Direction

Determining Direction of Blood

If more than one drop (from spatter) results, the point of origin can be determined

Blood Spatter > Direction

Determining Direction of Blood

This is a 2-dimensional point of origin.

It is possible to determine the 3-D point of origin

Blood Spatter > Direction

Determining Direction of Blood

The angle can be determined mathematically.

Width/Length, then take the inverse sin (sin-1).

This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)

Blood Spatter > Direction

For each blood drop, a string can be guided back to the point of origin.

Blood Spatter > Direction

Types of Spatter

Spattered Blood = random distribution of bloodstains that vary in size

Amount of blood and amount of force affect the size of blood spatter.

Can result from gunshot, stabbing, beating

Blood Spatter

Spattered Blood can:

Help determine the location of the origin of the blood source.

Help determine the mechanism which created the pattern.

Blood Spatter

Spattered Blood

In general, for higher impacts, the pattern is more spread out and the individual stains are smaller.

Low impact = beating

High impact = gunshot

Blood Spatter

Types of Spatter

Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot.

Not all gunshots will result in misting.

If misting is present, it is most likely a gunshot.

Blood Spatter

Gunshot Spatter

Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).

Blood Spatter

Types of Spatter

Beating and Stabbing Spatter = larger individual stains

First blow usually doesn’t result in spatter since there is not yet any exposed blood.

Blood Spatter

Types of Spatter

Satellite Spatter = free falling drops of blood that fall onto a spatter pattern.

These drips are usually much larger than impact spatter.

However, blood dripping into blood can create a spatter.

Blood Spatter

Types of Spatter

Castoff Pattern = Blood flung off of swinging object.

Can reconstruct where assailant and victim were positioned.

Blood Spatter

Types of Spatter

Expirated Bloodstain Pattern = Blood can accumulate in lungs, sinuses, and airway. Forcibly exhaled.

Can appear like beating or gunshot pattern.

May be mixed with saliva or nasal secretions.

Blood Spatter

Alteration of bloodstain over time

Blood dries and clots over time. Difficult to estimate the time the blood exited

the body. Clotted smears can indicate time of movement.

Blood Spatter