HOW IS BLOOD EVIDENCE USED IN FORENSICS?

How blood evidence is collected Blood pool –collect with gauze pad or clear cotton. Let air dry and refrigerate of freeze within 48 hours. Dried blood –wrap object in clean paper and place in paper bag. Small object, send whole object in. Large object, cover with paper and tape down or scrape it off with a knife. Swab

Bloodstain Patterns Physical Evidence Usually Found at Violent Crime Scenes Gives Clues as to WHAT Happened May Suggest Sequence of Events Analysis MUST be placed in context of all aspects of crime scene investigation in order to reconstruct (possible) criminal events.

Forensic Analysis of Blood 1. Visual examination of evidence 2. Presumptive screening test (Is it blood?) 3. Confirmation test (Seriously, is it blood?) 4. Determine species origin (human blood?) 5. Identify the blood (whose blood is it?)

Presumptive Screening Tests Negative result means the questioned stain is not likely blood Positive result means the questioned stain is likely blood

Presumptive Screening Tests Kastle-meyer - P henolphthalein Color test - Positive result = pink Still used today Used on dried blood False Positive – A positive result given by a substance that is not blood.

Presumptive Screening Tests Luminol Luminol is combined with oxidant and sprayed over area thought to contain blood Emits a blue-white to yellow green glow Used to locate and define areas of blood  old blood stains  cleaned floor More sensitive than color tests May damage blood stain (no blood/DNA typing)

Presumptive Screening Tests Luminol

Confirmatory Tests Due to the possibility of false positives with the presumptive tests, confirmatory tests are necessary Confirmatory tests involve making crystals that detect the presence of hemoglobin Requires a microscope Teichmann Test and Takayama Test

Genetic Markers in Blood If a stain is blood, and it is human blood, then whose is it? Precipitin determines if it is animal or human blood Blood Group Markers Protein/Enzyme Markers DNA (sometimes)

Introduction to Blood RBC = no DNA; WBC = yes DNA All blood cells have blood groups (antigens) on outside of cell. ABO Markers

Blood Group Markers ABO Markers (antigen and antibodies) Blood Type Antigen (blood group) Antibody % population A B AB O

Blood Group Markers ABO Markers (antigen and antibodies) Blood Type Antigen (blood group) Antibody % population AAAnti-B40 BBAnti-A10 ABA & Bnone5 OHAnti-A & Anti-B 45

Blood Group Markers ABO Markers A cells clump with anti-A B cells clump with anti-B AB cells clump with both O cells do not clump Rh clumping = +

Evidence may reveal: Speed with which blood left its source Distance of bloodstain from target Direction from which blood impacted Origin(s) of bloodstain Position of victim & assailant Weapon/Number of blows/shots Movement of victim & assailant

Splash 1 5 ml blood squirted from a syringe from a height of 1 m

Wipe Patterns Object moves through a wet bloodstain Feathered edge suggests direction

Transfer Patterns Wet, bloodied object contacts a secondary surface Transfer from: hand, fingers shoes, weapon hair Transfer to: walls, ceilings clothing, bedding Produces mirror-image of bloodied object

Transfer from hair 70

Flow Patterns Blood flows horizontally & vertically Altered by contours, obstacles Often ends in pool

Flow pattern

Tracing origin of blood spatter A. Angle of Impact B. Point of convergence C. Point of origin D. Source of spatter (type of weapon)

Blood Spatter (or splatter) Blood drops form different shapes and sizes Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

Dripping blood Can follow movement of victim and assailant Can show the speed of blood loss.

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

HEIGHT FALLEN Single drops of blood falling from fingertip onto smooth cardboard from various heights. No change in diameter beyond 7 ft.

Direction:Wave 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

Determining Direction of Blood  The angle of impact 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)

Real World!  What if blood drop is not a pretty oval?!? Do the best you can!!!

ANGLE OF IMPACT 90  10  70  20  30  60  50  40  Adapted from Introduction to Forensic Sciences, W. Eckert, CRC,  Gravitational dense zone at lower edge

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

Low Velocity velocity ≤ 5 ft/s stain size is (relatively) large: diameter ≥ 4mm examples: blood drops into blood and footstep spatters

Medium Velocity 5 ft/s ≤ velocity ≤ 25 ft/s stain size : 1 mm ≤ diameter ≤ 4mm examples: blood flicked off finger and blunt object used on victim

High Velocity velocity ≥ 100 ft/s (  68 mph) stain size (relatively small): diameter ≤ 1mm examples: gunshots and propellers

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

Tracing Origin of Bloodspots uses Point of convergence method 2 dimensional image Point of origin method –adds 3rd dimension to image In practice: –use of string & protractor at scene –use of computer at laboratory

POINT OF CONVERGENCE

Point of Convergence 5 ml blood squirted from a syringe from height of 1 m 17

POINT OF ORIGIN length width Angle of impact = arc sin W/L Distance from point of convergence Height above point of convergence Origin 85  60  45  30 

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

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

Gunshot: back& forward spatter Bloodstained foam held just above target surface. Back-spatter on entry Forward spatter on exit bullet Bullet passing L to R just above sheet Bullet enters foam bullet exits foam

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

Three overhead swings with hatchet

Example, cont’d ceiling

Cast off Pattern (2/2) 1 2 3