Bloodstain Pattern Analysis

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Josephine Shepherd
5 years ago
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1 Bloodstain Pattern Analysis Summary What is Blood? Determining Distance of Blood Types of Blood Stain Patterns What is Blood? 1

2 Introduction to Blood (or splatter) Blood drops form different shapes and sizes Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene. > Distance Blood drops fall as small spheres 2

> Distance Drops form circle when hitting surface Size depends on

(size) Higher distance = larger diameter Due to air resistance,

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

3 > Distance Drops form circle when hitting surface Size depends on speed of blood drop > Distance Faster drop = larger diameter (size) Higher distance = larger diameter Due to air resistance, speed maxes out at distances above about 7 feet > Distance However, size of drop also depends on the volume of the drop. Volume depends on the object blood originated from (needle = small; bat = large). 3

sphere Rough surface may cause some splatter

4 > Distance Since the volume of blood is unknown The distance a drop has fallen cannot be measured. Effect of Surface Smooth surface = smooth sphere Rough surface may cause some splatter > Direction Narrow end of a blood drop will point in the direction of travel. 4

5 > Direction If more than one drop (from spatter) results, the point of origin can be determined > Direction If more than one drop (from spatter) results, the point of origin can be determined > Direction This is a 2-dimensional point of origin. It is possible to determine the 3-D point of origin 5

6 > Direction 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) > Direction For each blood drop, a string can be guided back to the point of origin. 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 6

7 Spattered Blood can: Help determine the location of the origin of the blood source. Help determine the mechanism which created the pattern. 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 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. 7

8 Gunshot Spatter Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits). Beating and Stabbing Spatter = larger individual stains First blow usually doesn t result in spatter since there is not yet any exposed blood. 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. 8

Castoff Pattern = Blood flung off of swinging object. Can reconstruct where assailant and victim were positioned. Expirated Bloodstain Pattern = Blood can accumulate in lungs, sinuses, and airway.

9 Castoff Pattern = Blood flung off of swinging object. Can reconstruct where assailant and victim were positioned. 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. 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. 9

Blood spatter analysis

Blood spatter analysis the examination of the shapes, locations, and distribution patterns of bloodstains, in order to provide an interpretation of the physical events which gave rise to their origin History