Practical Crime Scene Ch. 10

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Crime Scene Investigation

Bloodstain pattern analysis is directed at evaluating the bloodstain patterns found in the scene in an effort to categorize them into

an established taxonomy

The primary categories for bloodstains are

passive and dynamic

Directionality is defined by

the long axis of the individual stain and the presence of scallops, tails, and small satellite spatter in the side opposite where the droplet first struck

The point of convergence is determined by

the reverse vector of the directionality of a number of stains in a pattern

A blood droplet in flight is a sphere and as a result any measurement of the diameter of the droplet will be

equal.

To determine the impact angle measure the long and short axis of the stain which will not include any

portion of the scallops or tail and then divide the short axis by the long axis.

The resulting number will always result in a number

less than 1.

The inverse SIN of the short axis/long axis

equals the impact angle

Long elliptical stains indicate an impact angle of

10 to 30 degrees

Bear claw-shaped stains suggest impacts between

40 and 60 degrees

Circular stains suggest impact angles between

70 and 90 degrees

Impact angle and directionality will suggest the

area of origin of the event

Bloodstain pattern analysis has established classifications of stains know as the

taxonomy of stains.

Bloodstain pattern evidence is almost always

class-characteristic evidence

Bloodstain patterns are grouped into two basic categories

passive stains and dynamic patterns

Passive stains result from an action other than a directed force to a blood mass. Examples include

contact stains, dripping blood, drip trails, and blood pools or flows.

Pattern transfer occurs when

an object wet with blood contacts another surface

Wipe pattern is a disturbance of

a preexisting bloodstain

Swipes patterns are produced when a bloodied object comes in contact with

another surface with associated lateral motion

Saturation stains rarely provide the CSI with

specific information

Dynamic patterns are created by

forceful events where blood is projected out from a source. They include spatter, castoff, arterial patterns, splashes, and spines

Spatter occurs when a blood mass is broken up into droplets and occur primarily as

impact spatter usually from gunshot or blunt trauma

Castoff patterns occur when an object is bloodied and then

moved or swung with some force

Arterial patterns result from blood in volume that is

projected into a scene under pressure from an artery or the heart

Splash patterns occur when a volume of blood is

projected into the scene with minimal force. Splash are not typical and may be present in staged crime scenes

Other patterns include

fly spots and void patterns,

Void patterns occur when a

secondary object is present between a bloodstain event and a nearby surface. They most often appear in spatter events.

Two primary presumptive blood tests are

phenolphthalein and leucomalachite green

phenolphthalein and leucomalachite green tests are based on

an oxidation-reduction of the chemicals that occurs in the presence of heme

During the use of the phenolphthalein test if any pink color reaction occurs in the second step and prior to applying oxidizer it would indicate

a false positive.

During the use of the phenolphthalein test if an immediate pink color reaction occurs after the application of the oxidizer (hydrogen peroxide) than

the test is positive for the presence of blood.

The same procedures are followed for leucomalachite green and a

green reaction will indicate a positive test.

Chemical enhancement of latent blood using luminol and fluorescien allow the visualization of latent bloodstain patterns that are

either too light or washed up

The primary methods for enhancing latent or slightly visible bloodstain are the use of

luminol, fluorescein, amido-black and leuco-crystal violet (LCV)

Luminol and fluorescein react in the presence

of heme.

A positive reaction with Luminol produces a

chemiluminescence

A positive reaction with fluorescein is observed only under an ALS

between 455 and 485 nm.

Amido black and LCV are both react to

proteins present in the blood

Firearms examiners deal with internal ballistics to

determine functionality of a weapon.

Firearms examiners look at a variety of individual and class to compare the characteristics of

bullets, casings, and weapons to one another.

Beyond comparison work

firearm examiners exam the following areas to assist in reconstructing the shooting incident,: evaluate ejection patterns, gunshot residue patterns, and examination of bullet and bullet fragments

Forensic pathologists deal with terminal ballistics and consider the effect of

projectiles on the body and provide information that may assist in limiting the position of the victim at the time of wounding.

Close contact

muzzle in direct contact with skin

Loose contact

extremely close proximity to skin

Intermediate range

muzzle is between 5 inches and 40 inches

Indeterminate range

no conclusion on muzzle range

CSI deal with external ballistics they consider the

trajectory of the bullet after leaving the weapon and deal with bullet defect verification, defining the bullet angle based on defect shape, and direction of fire.

The presence of metallic lead in a suspected bullet defect is evaluated on scene using

sodium rhodizonate test (Plumbtesmo).

The presence of metallic copper in a suspected bullet defect is evaluated on scene using

DTO dithio oximide (Cuperotesmo)

Minor axis divided by the major axis =

N

The inverse SIN of N is equal to

the approximate impact angle

The ellipse matching method in bullet defects will increase the

accuracy of defining the impact angle

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