Definition Bloodstain Pattern Analysis the examination of the
Definition • Bloodstain Pattern 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. – Based on the premise that all bloodstains and bloodstain patterns are characteristic of the forces that have created them.
Some facts about blood. . . 1. Adult humans have about 4 -5 L of blood 2. 40% blood loss causes death (internal or external loss) 3. Losing 1. 5 L can incapacitate a victim 4. Blood is viscous and has surface tension which causes it to form drops (blood molecules are attracted to each other. )
3 Categories of Blood Stains 1. Passive: Blood drips due to gravity A. B. C. D. Drops Drip patterns Pools clots
2. Transfer: bloody surface comes in contact with another surface A. Contact bleeding B. Swipe or smear C. Wipe D. Smudge
3. projected: due to force a. arterial/spurt b. Cast-off stains c. Impact spatter
A. Arterial: Bloodstain pattern(s) resulting from blood exiting the body under pressure from a cut artery.
B. Cast off stains: Blood released or thrown from a blood-bearing object in motion
C. Impact spatter: caused by the force of a blow. Fist, Knife Swinging Weapon Gun Important Info 1. Low velocity (force < 5 ft/sec), drops > 4 mm 2. Medium velocity (force ≈ 5 -25 ft/sec); drops 14 mm. 3. High velocity (force may be > 1000 ft/sec); drops < 1 mm – like mist
Target surfaces • Blood droplets that strike a hard smooth surface, like a piece of glass, will have little or no distortion around the edge. • Surfaces such as wood or concrete are distorted. Notice the spines and secondary spatter present.
Direction of blood drops • 90 degree angle; width = length • If blood strikes a surface at an angle <90˚ it is elongated. Pointed end is toward direction of travel.
• Angle of Impact
Point of Convergence • By drawing a line through the long axis of a group of bloodstains the point of convergence can be determined. • The point where the lines meet is the origin of the impact
Determining Height • Once we have determined the angle of impact & point of convergence, we can determine vertical height • Horizontal distance from drop to point of convergence = x • Vertical height (Y) = (X)(tan Θ) – Difficult in real life due to measurement error in W, L, & X – Horizontal initial velocity can cause error in measurements