Forensics & Genetics Unit 4: Blood (8.1-8.3)

Dr. Eduard Piotrowski

invented blood splatter analysis

• published the study of bloodstains in 1895

3 main blood types

A, B, O

Who discovered the 3 main blood types?

Karl Landsteiner

What replaced blood typing analysis in forensic science?

DNA profiling (typing)

What is blood type considered as?

class evidence

• cannot identify a specific person

3 components of blood

• red blood cells

• white blood cells

• platlets

red blood cells

carries respiratory gases

• transport oxygen from the lungs to the body's tissues

• carry carbon dioxide (CO2) waste from the tissues back to the lungs for exhalation

white blood cells

helps fight diseases & foreign elements

platlets

involved in repairing damage blood vessels (scabs)

• helps with blood clotting

What is the liquid the 3 components of blood are suspended?

plasma

plasma

carries antibodies, hormones, clotting factors, nutrients

(glucose, amino acids, salts, minerals)

antigen

foreign elements

antibody

assist in the immune system response by identifying & labeling foreign materials

What is the only blood component that can be used for DNA profiling?

white blood cells

agglutination

the clumping together of particles, like cells or bacteria, typically caused by specific antibodies binding to surface antigens

What happens if agglutination happens within someone’s circulatory system?

blood wouldn’t flow (blood would clump up)

Where are A & B antigens found?

red blood cells

What types of antigens are in Type A blood?

A only

What types of antigens are in Type B blood?

B only

What types of antigens are in Type AB blood?

both A & B

What types of antigens are in Type O blood?

none

Rh factor

protein on red blood cells

• independent of the A & B antigens

has Rh factor: Rh+

no Rh factor: Rh-

probabilty that someone has Type A Blood?

42%

probabilty that someone has Type B Blood?

12%

probabilty that someone has Type AB Blood?

3%

probabilty that someone has Type O Blood?

43%

probabilty that someone has Type Rh+ Blood?

85%

probabilty that someone has Type Rh- Blood?

15%

Why is eyewitness tesimoney not always reliable?

can’t recongize key elements

• can forget things

What steps does a CSI investigator take when it relates to blood evidence?

1) Secure the scene

2) Separate witnesses

3) Scan the scene

4) See the scene

5) Sketch the scene

6) Search for evidence

7) Secure any evidence

Blood

a suspension of blood components in plasma (mixture)

Why does blood stick together rather than break apart?

cohesion

• as a protective mechanism (coagulation) to stop bleeding upon injury

What shape will droplets of blood form with other forcing acting on them?

spherical shape (unless other forces act on it)

adhesion

attraction between molecules

• may form spines in the blood

How does adhesion affect the shape of a droplet of blood?

spines

jagged, spoke-like projections or disruptions radiating from the edge of a bloodstain

satellites

small droplets that detach from a main (parent) bloodstain

What is another force that could affect the shape on blood spatter?

when an artery is severed

What does the shape of a drop of blood provide?

evidence to the direction from where the blood originated

How does the shape of a droplet of blood vary?

from round to eliptical (longer than wide)

What will the pointed/elongated end of the blood indicate?

the direction of travel

passive drop of blood

when blood drips from a wound circular (without any force)

How will the droplet shape of blood change if it is dropped from an angle?

more eliptical shape

• more elongated as the angle changes

What does blood splatter size usually indicate?

weapon and type of injury

High intensity

100 ft/sec

• less than 1mm

• usually gunshot wounds

Medium intensity

25ft/sec

• 1-4mm

• usually beating ot stabbing

Low intensity

5ft/sec

• more than 4mm

• blunt object impact or dripping blood

How are blood stain patterns distinguished?

sixe, shape, & distribution pattern of a clutter of blood stains

What affects the shape of the droplets and distance the blood travels?

• velocity (speed) of the blood

• angle of impact

• surface characteristics

trail of circular, passive drops

linear pattern of round droplets of blood

ex.) a person walking while bleeding

cast off pattern

blood drops released form an object

• seen on walls or celiings

ex.) a person striking someone with a weapon

transfer pattern

bloody surface contacts a 2nd surface, minimum lateral motion

ex.) a person steps in blood or transfers blood from hand

wipe

a dry object moves through pre-exisiting blood with lateral motion

ex.) a hand wiping across a blood-spattered wall

swipe

when a bloody object moves across an unstained surface, leaving a feathered streak that shows the direction of motion

ex.) a bloody weapon dragged across a floor

arterial gush

caused by a severed artery, where blood is propelled out of the body at high pressure by the heart's pulse (large patterns)

expired blood

usually caused by blood from an internal injury mixing with air from the lungs being expelled through the nose, mouth or an injury to the airways or lungs

ex.) person with a broken nose that has bled into their airway

shadowing or void

an empty space (a "void") on a surface where blood spatter should be, indicating an object or person blocked the blood's path to that spot

area of convergence

the area containing the intersections generated by lines drawn through the long axes of individual stains that indicates in two dimensions the location of the blood source.

angle of impact

the acute angle formed when blood strikes a surface

area of origin

the three-dimensional location, including height, from which blood spatter originated