CH 9 / CH 10 (Impression Evidence) / (Bloodstain Pattern Analysis)

Types of Impressions

- Evidence (unknown/ looking for suspect )

- Elimination (first responders)

- Known (suspects)

Recovering impression evidence

- Prints

- Photography

- Lifting Impressions

- Chemical Enhancement

- Dental stone

Recovering prints involves

- Patent; (visible) blood / tire skid marks

- Latent; (not visible) oblique lighting needed

- Plastic; (3D) mud

When recovering prints, photographs must be

Examination quality; scale and proper lighting

When lifting impressions

Patent or latent prints > can be lifted by

- electrostatic lifting, only for 2D prints

- adhesive (for knowns), guys its just tape

Chemical enhancements of impressions

- Latent; luminescence (luminol may be used) & dye

- Plastic; snow print wax

Dental stone is

For plastic impressions

Examination of Tread Design looks at

- Class & Individual characteristics

- Tire position (straight or in turn)

Class Characteristics refers to

A tread's design, size, and shape

Individual characteristics refers to

wear marks and physical damage

Tire position straight refers to

Rear width only (rear tires track over the front)

Tire position in turn refers to

- Front and rear widths (they track seperately)

Identification of impressions is done through

Comparisons; overlay or side by side (SICAR database)

Biological properties of blood are either

- Non-cellular

- Cellular

Non-cellular consists of

Plasma; electrolytes and antibodies

Cellular consists of

- Red blood cells; transport O2

- White blood cells; fight diseases

- Platelets; clot formation

Exsanguination

Bleeding to death

Physical properties of blood consists of

- Surface tension

- High viscosity

Surface tension

Force that pulls liquid towards itself

High viscosity

Resistance to flow

What can affect spatter?

Surface texture

Impact spatter (is in relation to a shooter rather than the victim)

- Pattern occurs when an object impacts the source of blood

- Forward spatter

- back spatter

Forward spatter

exit wound / (away from a shooter)

Back spatter

entrance wound (hitting back / back splash) different from castoff

Velocity of force changes the pattern

- Low-velocity

- Medium-velocity

- High-velocity (is not always but does include misting; gunshot spatter)

Origin of impact patterns consists of looking at

- Tail of bloodstain

- Angle of impact

- Uses measurements from parent drops

- Area of convergence

- Area of origin

Tail of bloodstain points to the direction of

Travel

Angle of impact is the

Angle at which the blood hit a surface

Area of convergence is

(2D) found by drawing a straight line through bloodstain opposite of the tail

Area of origin shows

(3D) About where the blood spatter originated - aka the purpose of analysis

Castoff patterns are

Created from subsequent blows to a wound

(If a hammer is used as a weapon when the hammer is swung back a second time the blood that flies from the hammer is castoff)

Projected bloodstain patterns are

Patterns made when blood moves faster than gravity

- Expirated

- Arterial

Expirated (projected) patterns happens when

Blood accumulates in airway passages

(visually, looks like the blood has bubbles)

Arterial (projected) patterns happen when

Major arteries are cut

(visually, looks like large spurts of blood that was pumped out every time the heart was beating)

Transfer patterns happens when

wet blood comes into contact with an object (patent print)

Bloodstains change due to

- Drying (time/ if outside)

- Color change / oxidization

- Moisture (raining = loss of evidence)

- Void areas; object blocks deposits of blood