# Blood Stain

Pages: 5 (740 words) Published: March 25, 2013
Module 16
Blood Stain Patterns
Blood Volume
8% of body weight
4 – 5 liters female
5 – 6 liters male
40 % blood loss usually causes death
1.5 liter blood loss can incapacitate
Blood Stain Evidence
Biblical murderer Cain
Abels blood on the ground cried out Cains guilt
Abel is the first documented murder
Cain is the first documented murderer victim
The bloodstain patterns left by falling, projected or smeared blood can be analysed by trained crime scene investigators. Careful observation and measurement of the position and shape of bloodstains can give precise information about the direction of travel, angle of impact and the speed or velocity of the blood droplets. Gravity

Gravity - is acting on blood (without the body's influence) as soon as it exits the body. Given the right circumstances blood can act according to ballistic theory. Viscosity
Viscosity - is the amount of internal friction in the fluid. It describes the resistance of a liquid to flow. Surface Tension
Surface tension - is the force that gives the ability to blood to maintain its shape. When two fluids are in contact with each other (blood and air) there are forces attracting all molecules to each other. Surface tension

Surface tension enables blood droplets to maintain a sphere shape. Surface tension
Surface tension is an upwards force that enables insects such as a water strider to “walk on water”. Blood Stain Pattern
Recognition / analysis
Systematic form of analysis
Mathematical basis
Used in conjunction DNA analysis
Process of crime scene reconstruction
Blood is a fluid that makes up approximately 8% of the weight of a human body. Females have approximately 4-5 litres while males have between 5-6 litres. Blood is made up of cells (red blood cells and white blood cells) plus platelets in a yellowish liquid called plasma. Plasma contains gases (oxygen, carbon dioxide) and molecules such as proteins, fats and carbohydrates (sugars). Dr Edward Piotrowski scientist published “ Concerning the origin, shape , direction and distribution of bloodstains following head wounds caused by blows…first scientist to recognize the value of bloodstain interpretation Experimented in 1895 with rabbits blood

First used in the 1940s for police purposes
Recognition
It may be blood but does it have significance ?
Will one droplet tell us anything ?
Passive Stains
Blood Dripping Into Blood
Displacement
Dispersion
Retraction
Height and size of blood drops
A blood droplet released from a 1m height will be smaller than a blood droplet released from a 1.5m height. This is because the velocity of the blood droplet released from a higher height is greater. 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, propellers, fans
Expiratory
blood
High Velocity
Projected Stains
Angle of Impact
Stain Patterns
Blood dropping onto fabric
Stain Patterns
Blood on tile floor
Ghost outline
Stain Patterns
Arterial gushing
Stain Patterns
Contact bleeding
Transfer Stains
Blood Source
Source of contact bleeding
Blood Swipe
Stain Patterns
Swipe
Multiple Pattern
Stain Patterns
Swipe
Stain Patterns
Transfer stain
Stain Patterns
Stain Patterns
Passive stains
Drip Patterns
Back Spatter
Back spatter
Low velocity impact spatter
Expiratory blood stain
Fine mist of blood with no significant large droplets.
Protection – Personal
Avoid unnecessary contact
Footwear protection
Biohazard suits
Protection - Contamination
Change gloves frequently
Change gloves after each sampling
In order to identify a human DNA profile you require a...