crime scene reconstruction: forensic bloodstain pattern analysis chapter 10
TRANSCRIPT
CRIME SCENE RECONSTRUCTION:
FORENSIC BLOODSTAIN PATTERN ANALYSIS
Chapter 10
10-2©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Vocabulary Terms• Angle of impact
• Area of convergence
• Area of origin
• Arterial spray
• Back spatter
• Cast-off
• Drip trail pattern
• Expirated blood pattern
• Flow pattern
• Forward spatter
• High velocity spatter
• Impact spatter
• Low velocity spatter
• Medium velocity spatter
• Parent drop
• Satellite spatter
• Spine
• Skeletonization
• Transfer pattern
• void
10-3©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Crime Scene Reconstruction• The method used to support a likely sequence of events by
the observation and evaluation of physical evidence as well as statements made by those involved with incident. – Medical examiners– Criminalists– Law enforcement
• All parties recover physical evidence and sort out the events surrounding the occurrence of a crime.
10-4©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
http://www.crimescenetwo.com/img/popup/book2p2.jpg
Source: http://science.howstuffworks.com/bloodstain-pattern-analysis1.htm
Bloodstain Pattern Analysis (BPA)What can an investigator learn from the analysis of a blood spatter? Type & velocity of weapon # of blows Handedness of assailant (right or left-handed) Position & movements of the victim and assailant during and after the attack Which wounds were inflicted first Type of injuries How long ago the crime was committed Whether death was immediate or delayed
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Stain Patterns of Blood• CSI responsibilities:
– location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the events that produced the bleeding.
• Surface texture and the stain’s shape, size, and location must be considered when determining the direction, dropping distance, and angle of impact of a bloodstain.
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Stain Patterns of Blood• Surface texture
– In general, the harder and less porous the surface, the less spatter results
• Wood vs. marble
• Direction of travel of blood striking object– Pointed end of a bloodstain always faces its direction of
travel
• Impact angle of blood on a flat surface can be determined by measuring the degree of circular distortion– @ right angles the blood drop is circular– As the angle decreases, the stain becomes elongated.
10-7©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Height/Surface
Single drop of blood falling from various heights (m) onto various surfaces
smooth floor paper towel fabric
0.5
1
2
3
0.5
1
2
3
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Lines of Convergence• Draw straight lines down
the long axis of splatter & notice intersection
• Origin Point
– The intersection or point of convergence of the lines represents the origin point.
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Point of ConvergencePoint of Convergence16
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
• Bloodstain Analysis
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Stain Patterns of Blood• A shooting may leave a distinct gunshot spatter
pattern. – Forward spatter from an exit wound – Back spatter from an entrance wound.
• Amount of back spatter depends on– location of injury– size of the wound created– distance between the victim and the muzzle of
the weapon
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Gunshot: back& forward spatterBloodstained foam held just above target surface.
Back-spatter on entry
Forward spatteron exit
bullet
Bullet passing L to R just above sheet
Bullet enters foam
bullet exits foam
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Back spatter on steadying
hand
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Arterial Spurt PatternArterial Spurt Pattern• Blood exiting body under arterial pressure• Large stains with downward flow on
vertical surfaces• Wave-form of pulsating flow may be
apparent
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Small arterial spurt
spatter
broken pottery
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Cast-off From Weapon• A cast-off pattern is created when a blood-covered object flings blood
in an arc onto a nearby surface
• First blow causes bleeding
• Subsequent blows contaminate weapon with blood
• Blood is cast-off tangentially to arc of upswing or backswing
• Pattern & intensity depends on:
– type of weapon
– amount of blood adhering to weapon
– length of arc
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Downswing of HammerDownswing of Hammer24
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Cast-off from WeaponCast-off from Weapon
ceiling
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Wave Cast-offWave Cast-off
.Parent drop
wave cast-off
Tail of wave cast-off points back to parent drop
Tail of elongated stain points in direction of travel
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Trapped!
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Impact Bloodstain• Low velocity (5 ft/s, 1.5 m/s; >3mm drop)
– e.g. free-falling drops, cast off from weapon
• Medium velocity (5-25 ft/s, 7.5 - 30 m/s; 1-3mm drop)
– e.g. baseball bat blows
• High velocity (100 ft/s, >30 m/s; < 1mm drop)
– e.g. gunshot, machinery
10-22©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Medium velocity blood spatter.Point of impact 15 cm in front of vertical target surface
6” ruler
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10-23©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Angle of ImpactAngle of Impact90
10
70
2030
60 50 40
Adapted from Introduction to Forensic Sciences,W. Eckert, CRC, 1997
80
Gravitational dense zoneat lower edge
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
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Stain Patterns of Blood• Expirated blood pattern
– pattern created by blood that is expelled from the mouth or nose from an internal injury
• Void – created when an object blocks the deposition of blood
spatter onto a target surface or object.
• When an object with blood on it touches one that does not have blood on it, this produces a contact or transfer pattern. – fingerprints, handprints, footprints, footwear prints,
tool prints, and fabric prints in blood.
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Stain Patterns of Blood• A pool of blood occurs when blood collects in a level (not
sloped) and undisturbed place.
• Flows– Patterns made by drops or large amounts of blood
flowing by the pull of gravity
• The edges of a stain will dry to the surface, producing a phenomenon called skeletonization.
• Trail pattern– A series of drops that are separate from other patterns,
formed by blood dripping off an object or injury.
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
Flow pattern72
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FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
• Passive Bloodstains– Patterns created from the force of gravity– Drop, series of drops, flow patterns, blood pools, etc.
• Projected Bloodstains– Patterns that occur when a force is applied to the source of
the blood– Includes low, medium, or high impact spatters, cast-off,
arterial spurting, expiratory blood blown out of the nose, mouth, or wound.
• Transfer or Contact Bloodstains– These patterns are created when a wet, bloody object comes
in contact with a target surface; may be used to identify an object or body part.
– A wipe pattern is created from an object moving through a bloodstain, while a swipe pattern is created from an object leaving a bloodstain.
Images from http://www.bloodspatter.com/BPATutorial.htm
Blood Spatter Movie
Types of Bloodstain Patterns
10-29©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
How is Blood Evidence Detected?• UV lights to help find traces of blood & other bodily fluids
that are not visible under normal lighting conditions.
• Blood Reagent Tests (Presumptive tests)
• Detects hemoglobin in the blood. – Phenolphthalein (Kastle-Meyer test) and produces a pink color
when it reacts with hemoglobin.
– HemaStix is a strip that has been coated with tetramethylbenzidine (TMB) and will produce a green or blue-green color with the presence of hemoglobin.
10-30©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458
FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein
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Documenting Bloodstain Evidence
• Investigators should – Note, study, and photograph each pattern and drop of
blood– Accurately record the location of specific patterns– The investigator should create photographs and
sketches of the overall pattern
• Two common methods of documenting bloodstain patterns are the grid method and the perimeter ruler method.