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52 terms

Practical Crime Scene Ch. 10

Crime Scene Investigation
STUDY
PLAY
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