fs ch 9

Chapter 9

Bloodstain Pattern Analysis

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

All Rights Reserved.2

General Bloodstain Features

Valuable insights for investigators

Ceilings/floors/walls Location

Distribution

Appearance




General Bloodstain FeaturesInfo from blood stains:

Direction Angle Location of victim Movement Number of blows Location of suspect




Effects of Surface Texture

Determining direction/distance/angle:ShapeSizeLocationSubstrate: Hard/non-porous-less spatter




Directionality and Angle of Impact

Direction:-pointed end (tail) always faces direction of

travel

Impact angle:-measuring the degree of circular distortion-right angles the blood drop is circular-as angle decreases-stain elongates

-equation:Width = AngleLength




Impact Bloodstain Spatter Patterns

Forward spatter:-outward/away

Back spatter (blow-back):-backward




Classifying Impact Spatter Low Velocity Spatter:-3 mm or >-minimal force (<5 ft/sec)

Medium Velocity Spatter:-1-3 mm-5 to 25 ft/sec

High Velocity Spatter:-< 1mm-100 ft/sec or faster




Low Velocity

You can only swing a hammer so fast by hand.




Low Velocity

Same with a pipe




High Velocity

Fine mist-smaller particles. Indicates fast force.




Yuck

High velocity spatter after a homicide bomber detonated a bomb suit he was wearing.

SPLAT!!!




Blood spatter

High impact




Area of Convergence

Area of convergence:

-point on a two-dimensional plane-drops in impact pattern originated-draw straight lines through long axis of

several bloodstains-following the tails




Area of Convergence

Blood stains on a wall.




Area of Origin Area of origin:

-the area in a three-dimensional space from which the blood was projected

-shows the position of the victim/suspect in space

-string method approximates the position of the area of origin using angles of impact of stains




Area of Impact

String method. I do not understand the pillow on the wall. What position was the victim in when the incident occurred?




Gunshot Spatter

Gunshot Spatter:-fine forward spatter-exit-back spatter-entrance-only if the bullet does

not exit the body

Drawback effect:-depends on distance from the weapon

discharged-some back spatter may strike the

gunman/enter the gun muzzle




Cast-off Spatter Cast- Off:

-blood-covered object flings blood in an arc onto surface

-commonly produced by a bloody fist or weapon between delivering blows

-features affected by size of object/amount of blood/direction object moving

-counting and pairing forward/backward patterns determine the minimum number of blows




Arterial Spray Spatter Arterial spray:

-pressure of arterial wound pumping blood out of injured area

-injury site begins with the biggest spurt

-trail shows the victim’s movement

-oxygenated blood brighter red than blood from impact wounds




Arterial Spatter

You can determine the victim’s movements after the injury.




Expirated Blood Patterns Expirated blood pattern:

-blood expelled from mouth/nose from an internal injury

Presence-important clues:-injuries suffered -events




Void Patterns Void pattern:

-created when object/person blocks deposition of blood spatter onto target surface

-spatter deposited onto the object/person-blank space clue as to the size/shape of

object/person-body position of the victim/assailant




Contact/Transfer Patterns

Contact/transfer pattern:-object with blood touches surface without

blood-Simple transfer patterns:-object makes contact with and is removed

without any movement of the object-size/general shape of object may be seen in

simple transfer-Other transfers-movement of the bloody

object across a surface




Transfers

Contact transfer of bloody hand




Transfers

Contact transfer of bloody foot print




Flows Flow patterns:

-drops/large amounts of blood flowing-Active-actively bleeding wound-Passive-blood deposited on surface (arterial

spurt) -direction-shows movement of

objects/bodies while flowing/dried-interruption of a flow

pattern-sequence/passage of time between the flow/interruption




Pools Pools:

-collects in level/undisturbed area-absorbent surface-absorbed throughout the

surface/diffuse-approximate drying time is related to the

environmental conditions-analyst may be able to reasonably estimate

the drying times of stains of different sizes




Skeletonization

Skeletonization:

-edges of stain dry to surface-50 seconds of deposition of droplets-longer for larger volumes-if bloodstain is altered by a contact of wiping

skeletonized perimeter left intact-skeletonization time-determine timing of

movement/activity




Trail Patterns Trail pattern:

-series of drops dripping off object/injury

-form line/path usually made by the suspect

-show movement/lead to discarded weapon/provide identification of the suspect by own blood

-shape of stains determine direction/speed person was moving




Blood trails

Big one




Documenting Bloodstain Evidence Note/study/photograph-each pattern/drop-accurately record locations of specific

patterns-distinguish stains from which laboratory

samples were taken-photographs techniques:-grid method- grid of squares of known dimensions

over entire pattern-perimeter ruler method-rectangular border of

rulers around pattern/placing a small ruler next to each stain




Interpreting Bloodstain Evidence

Certified in interpretation:-40 hour course

Imperative:-all personnel familiar with patterns to

properly record/document

fs ch 9

Sports

angle of impact direction

spatter blow

angle length

angle decreasesstain

bloodstain pattern analysis

shape size location

blood stains

blood drop