Criminalistics exam 2

Ballistics, Firearm and toolmark PSP, Blood, Blood stain, Biological evidence, shoe & tire

Rifiling

the spiral cut on the internal surface of the barrel of a rifle or pistol and some shotgun barrels

Rate of twist

the distance the projectile needs to travel down the barrel to complete one full revolution

Lands

the projecting component of rifling

Semi-automatic

fires and reloads itself before firing another shot

Wad

part of a shell that separates shot and propellant

Soot

burnt propellant consisting mainly of carbon

Pitch

refers to the angle that rifling is cut into the barrel

Gauge

smooth barrel firearms or shotguns. number of round lead balls of the diameter of the interior of the barrel required to weigh one pound

Chain of custody

documentation of all evidence

Locards’s exchange principle AKA…?

Theory of exchange

Stippling

deposition of fragments of powder. abrasions caused by the impact of unburnt particles of powder impacting the skin

Spatter

The description of a stain that results from blood hitting a target

Serum

The liquid that separates from blood when a clot is formed

angle of impact

also known as angle of incidence; the acute angle created by the intercept of the target with the droplet’s vector

Blunt force

typically causes medium velocity spatter and impact spatter

Sharp force

will typically cause low velocity spatter as well as impact spatter

Projectile

the component of the cartridge that is fired from the barrel and eventually hits a target

Tool

an object used to act on and leave marks on another object

Projected

a bloodstain pattern resulting from the ejection of a volume of blood under pressure

cause cast off, arterial, and expirated patterning

Cast-off

a bloodstain pattern resulting from blood drops released from an object due to its motion

Expirated

a bloodstain pattern resulting from blood forced by airflow out of the nose, mouth, or a wound

Aerial

a bloodstain pattern resulting from the ejection of a volume of blood from a breached artery

Secondary

type of spatter pattern

Satellite spatter

a smaller bloodstain that originated during the formation of the parent stain as a result of blood impacting a surface/blood dripping into blood

Swipe

a bloodstain pattern resulting from the transfer of blood from a blood-bearing surface onto another surface, with characteristics that indicate relative motion between the two surfaces

Wipe

an altered bloodstain pattern resulting from an object moving through a pre-existing wet bloodstain

Drip

a bloodstain resulting from a falling drop that formed due to gravity

Saturated Stain

a bloodstain resulting from the accumulation of liquid blood in an absorbent material

Pool

A bloodstain resulting from an accumulation of liquid blood on a surface

Flow

a bloodstain pattern resulting from the movement of a volume of blood on a surface due to gravity or movement of the target

Impact spatter

A bloodstain pattern resulting from an object striking blood

Clot

gelatinous mass formed by fibrinogen, platelets and other clotting factors

Expiratory stain

A bloodstain pattern resulting from blood forced by airflow out of the nose, mouth, or a wound.

May have bubble rings or mucus or appear diluted

Can be tested for amylase to detect saliva

Void

an absense of blood in an otherwise continuous bloodstain or bloodstain pattern

Fly spots

bloodstains resulting from fly activity that may mimic other bloodstain patterns

Splash

a bloodstain pattern caused by a low velocity impact on a surface

Spine

pointed edge characteristics that radiate away from the center of a bloodstain; formation depends on velocity and surface texture

Parent stain

original stain that satellite spatter forms from

Arterial gush

blood exiting the body under pressure from a breached artery

Patent prints

prints that are visible to the naked eye

What are the categories of blood stains?

Passive stains, Spatter, Altered stains

Do blood stains ever change color?

Yes, relatively fresh blood is reddish brown, Thin layers may appear grayish green, or may assume other colors from black to blue to greyish-white

High velocity blood spatter would most likely be caused by what type of trauma?

Gunshot

What is a blood stain? (full def)

Transfer resulting when liquid blood comes into contact with a surface or a moist or wet surface comes into contact with dried blood

What are the 4 current blood types?

A, B, AB, O

What are the original blood typing names? who created them?

A, B, C created by Dr. Karl Landsteiner in 1900

List examples of passive staining

transfer, flow, swipes, drops, large volume

What is the difference between forward and backward spatter?

Forward spatter is a bloodstain pattern resulting from the blood drops that travelled in the same direction as the impact force

Backward spatter is a bloodstain pattern resulting from the blood drops that traveled in the opposite direction of the external force applied

List some common substances that are easily mistaken as blood stains

Paint, pigments, rust, tobacco, snuff, urine, feces, coffee

What is a transfer stain

a bloodstain resulting from contact between a blood bearing surface and another surface

What are the three preliminary steps of identifying a suspected bloodstain?

1- Visual

2- Presumptive

3- Confirmatory

Describe presumptive step of identifying a suspected bloodstain

In field tests, Phenolphthalein, Leucomalachite green, ortho-tolidine, tetramethylbenzidine (TMB), luminol, fluorescein

Describe Confirmatory step of identifying a suspected bloodstain

Is it blood? - teichmann test

Is it human blood? - ring precipitin test

Whose blood is it? - A,B,O blood typing, DNA, protein/enzyme markers

Describe Visual step of identifying a suspected bloodstain

Using your human senses and judgement

What is a visible impression? provide examples

occurs when footwear steps into foreign substance and is contaminated by it, then comes into contact with a clean surface and is pressed onto it. ex = bloody footprint

What is a Plastic impression? provide examples

occurs when footwear steps into a soft surface such as deep mud, snow, wet sand or dirt creating a three dimensional impression. ex footprint in snow

What is a latent impression? provide examples

impression that requires processing to see most often found on smooth surfaces.

What are methods for documenting visible impressions?

photography, sketching

What are methods for documenting plastic impressions?

photography, casting

What are methods for documenting latent impressions?

lifting

There are three evidentiary considerations to account for in footwear and tire
impressions what are they?

Changing Characteristics → unlike fingerprints, shoes and tires can change
Time Lapse → avoid delay to protect significance of recovery
Partial Prints and Impressions → in most causes ~70% of a partial heel print contains 10 or more times the identification points of a set of fingerprints left at a crime scene

What are the differences between prints and impressions

prints are 2d impressions are 3d

On what surfaces might you find footwear and tire impressions?

mud, dirt, snow, sand

On what surfaces might you find footwear and tire prints?

hard smooth surfaces, asphalt, concrete, flooring, etc

Define visible footwear evidence

Occurs when footwear steps into a foreign substance
and is contaminated by it, then comes into contact
with a clean surface and is pressed onto it

provide examples for what materials may create visible footwear evidence

mud, blood, sand, dust, snow etc

What types of surfaces are latent footwear impressions usually found on?

hard smooth non porous surfaces

What are the four methods of tire/footwear evidence documentation? name and describe each

photography, taking pictures/videos

sketching, self explanatory

casting, creating a mold of impression

lifting, very similar to taking finger prints

what are some reasons why footwear impressions are easily overlooked? (6)

lack of training, undervalued/not understood, belief that impressions have been walked or driven over, incomplete searches, weather, intentional destruction

What are the class characteristics of footwear evidence?

brand, size, style, possible gender

What are the class characteristics for tire evidence?

brand, radial width, tread design, tread dimension, noise treatment, wear patterns

What are the individual characteristics for footwear evidence?

cuts, scratches, gouges, tears, physical damage

what are the individual characteristics for tire impressions?

cuts, scratches, gouges, tears, physical damage, random identifying characteristics

Will tire evidence mostly consist of prints or impressions?

impressions

What is the discipline of ballistics?

the branch of physics that deals with the flight if projectiles

Difference between single action and double action (IDENTIFY PICTURES)

single = handgun cocked by drawing back hammer

double = pulling trigger both cocks and fires gun

Be able to define, differentiate, and provide examples of individual characteristics of firearms

random imperfections, number of lands/grooves, diameter/width of lands/grooves, depth of grooves, direction of rifling twist, pitch, angle of twist

What creates individual characteristics of firearms?

tool surface and manufacturing

Define caliber

determined by diameter of projectile or bore measured in 1/100th in or mm

What does caliber refer to?

designate ammunition for use in refiled firearms

How is caliber determined/measured?

powder charges and cartridge length, not size of projectile fired

What features of a gun/bullet lead to determination of caliber

diameter

What is armalite?

a rifle company

What is Armalite commonly abbreviated as?

AR

What kinds of analysis do these forensic examiners perform?

functionality examinations, examine discharged cartridges, restoring serial numbers, generate report, testify when requested

What bloodstain pattern is this?

Expiration pattern (spatter projected)

What bloodstain pattern is this?

Impact spatter

What bloodstain pattern is this?

Forward spatter (spatter impact)

What Bloodstain pattern is this?

Back spatter (spatter impact)

What bloodstain pattern is this?

Arterial pattern (spatter projected)

What bloodstain pattern is this?

Cast off (spatter projected)

What bloodstain pattern is this?

Drip pattern (passive)

What bloodstain patterns are shown here?

a parent stain and satellite spatter (spatter secondary)

What bloodstain patterns are these?

Transfer pattern (passive)

what type of bloodstain patterns are these?

Transfer pattern (passive)

What bloodstain pattern is this?

Swipe pattern (passive)

What bloodstain pattern is this?

Swipe pattern (passive)

What bloodstain pattern are these?

Swipe pattern (passive)

What bloodstain pattern is this?

flow pattern (passive)

what bloodstain pattern is this

flow pattern (passive)