Forensics exam 1

Define Serology

characterizationThe science of body fluid identification and characetization by examining blood, semen, saliva, and urine through the use of presumptive tests and confirmatory tests

What are the first two steps of Serology

1. Starts with suspects or victims clothing, weapons, and other items that may be evidence

2. Cuttings and swabs are taken from these pieces of evidence

From what years was forensic serology the most popular forensic lab procedure? What was it replaced with?

Forensic serology was the most important forensic lab procedue from 1950 to the 1980s. It was replaced with DNA techniques and labs. However, with limited funds and the time DNA testing takes, many labs still use basic serology tests.

What are the characteristics and functions of Plasma

Plasma is the straw colored, nonliving portion of the blood. It makes up 55% of an individuals total blood volume, while being 90% water and 10% salts, proteins, amino acids, enzymes, and hormones.

Plasma transports blood cells, products of digestion, and hormones throughout the body.

What portion of blood volume is consists of cells

45%

What are the characteristics of Erythocytes (RBC)

RBC distribute oxygen throughout the body and are used as a classical piece of forensic evidence (serology detection)

What are the characteristics of Leukocytes (WBC)

WBC are the only portion of the blood which carries DNA (only BC to have a nucleus). Due to carryinf DNA, WBC are used for inividial evidence

They are the “cleaning system” for the body, ridding it of pathogens.

What are the characteristics of Thrombocytes (platelets)

They are responsible for blood clotting

What is Serum as related to blood volume

Serum is the liquid that separates from the blood when a clot is formed

What is a Presumptive Test

A presumptive test is a chemical test that uses a change in color to detect the POSSIBLE presence of blood. This is a fast reaction, however it is nonspecific to humans

What presumptive test for blood IS specific to humans

LUMINOL tests

Explain the Kastle Meyer Presumptive test

1. A possible blood sample is swabbed

2. A drop of phenolphthalien reagent is added to the cotton swab

3. A drop of hydrogen peroxide is added to the same swab

4. If the cotton swab turns pink, the sample is blood. If there is no color change, the sample is not blood

Explain how a Presumptive phenolphthalein test works

The hemoglobin in blood posseses peroxidase-like activity that can oxidize phenophthalien to produce a pink color. Hemoglobin + phenolphthalien + Hydrogen peroxide will produce a bright pink color, indicating a possible blood sample.

However, copper, broccoli, and fruit juice can provide false positives. And this test is nonspecific to humans

What are the three confirmatory tests for human blood

1. Luminol

2. Takayama Stain

3. Ouchterlony test

What is luminol by definition used for

Luminol is a chemical used to detect trace amounts of blood left at crime scenes through a strong blue glow

Explain how luminol tests work

Luminol tests detect Iron in hemoglobin, not blood itself. Hydrogen peroxide and luminol are the principal players in the chemical reaction, but to produce a strong glow a catalyst (Iron) must be present.

Luminol is capable of detecting bloodstains diluted up to 300,000 times and doesn’t affect DNA testing

What is an Ouchterlony test

A confirmatory test that uses antibody reactions to determine if blood is human

Describe the takayama crystal test

A confirmatory test for blood that uses the formation of crystals to indicate the presence of blood

What test can be done to determine if a blood sample is animal or human

A preciptin test

What are the steps to the Preciptin test

1. Blood sample is injected into a rabbit to form antibodies

2. The rabbits blood is extracted as an antiserum

3. The antiserum is placed on the sample blood

4. The sample will react with human proteins if human blood is present

This test is very sensitive, so only a small amount of blood is needed

What is a key difference between human and animal blood cells

Animals have large nucleic RBC while humans have millions of RBC that do not carry a nucleus

What are the three ways that an individuals blood type may change

1. Bone marrow transplant

2. blood transfusion

3. bacterial infection

What is the Acquired B Phenomenon

As a result of a bacterial infection, the intestines produce an enzyme that alters the A blood group molecule to closely resemble the B molecule. This often affects patients with colon cancer, bowel obstructions, or sepsis

What are the five steps of scene pattern reconstruction

1. Stain condition

2. Pattern

3. Distribution

4. Location

5. Directionality

What are the five steps of lab result reconstriction

1. Genetic marker typing

2. age determination

3. source determination

4. race determination

5. sex determination

What is the feild of blood spatter evidence

A field of forensic investigation which deals with the physical properties o fblood and the patterns produced under different conditions because of various forces being applied to the blood

Blood follows the laws of physics

What are the four characeristics of blood droplets

1. A blood droplet remains
spherical in space until it
collides with a surface.

2. Once a blood droplet impacts
a surface, a bloodstain is
formed.

3. Droplets falling from the
same height, hitting the same
surface at the same angle,
will produce stains with the
same basic shape.

4. How will the shape change
as the height is increased or
decreased?

What is the general volume of blood droplets

0.03 cc to 0.15 cc

What conditions affect the shape of a blood droplet

1. Size of the droplet

2. Angle of impact

3. Velocity at which the droplet left its origin

4. height

5. texture of the target surface

What are three questions that can be answered by blood spatter interpretaton

1. The point (s) or origin of the blood

2. The type of weapon used

3. The type and direction of impact that produced the bloodshed

Bloodstain terminology: define the angle of impact

the angle at which blood strikes a target surface

Bloodstain terminology: define bloodtrain transfer

when a bloody object comes into contact with a surface and leaves a patterened blood image on the surface

Bloodstain terminology: Define Backspatter

blood that is directed back toward the source of energy

Bloodstain terminology: define cast-off

blood that is thrown form an object in motion

Bloodstain terminology: define contact stain

bloodstains caused by conact between a wet blood bearing surface and a second surfacet hat may not have blood on it

Bloodstain terminology: define directionality

related to the direction a drop of blood travels in space from its original point of origin

tapered end points in the direction of travel

Bloodstain terminology: define terminal velocity

the greated speed to which a free falling drop of blood can acceletate in the air

What are the four characteristics of High Velocity bood spatter

1. Greater than 25 feet per second

2. gives a fine mist apperance

3. consists of a colelction of small blood droplets

4. indicated a gunshot, coughing, sneezing, or explosives

What are the three characteristics of medium velocity blood spatter

1. Velocity of 5-25 ft/s

2. May inducate blut force trauma

3. May indicate cutting/stabbing motion

What are the three characeristics of Low Velocity Blood Spatter

1. Velocity of 5 ft/s or less

2. Indicates blood dripping from a weapon or wound

3. Drops are larger than 3mm in diameter

What does a round blood drop indicate

the blood drop fell at a 90 degree angle

what does an elliptical blood drop indicate

the blood was dropped from a less than 90 degree angle

What are the characteristics of these blood droplets in relation to the angle in which they fell

1. With the elongated tail, at 10* it is easier to determine the direction of travel that the blood droplet took

2. At about 30* the stain starts to produce a tail, indicating direction of travel

3. At 40* there is a slight tail

4. At 90* the droplet is perfectly round

Blood stain patterns: Radical Patterning

Resuts from blood pooling IN an open wound

Blood stain patterns: Pooling

Blood that collects in a puddle

Blood stain patterns: Arterial Spurts

Results from a wound to a major artery

Blood stain patterns: Cast-off (arc)

Blood from a weapon casts off onto ceilings and walls from preperation for another blow

Blood stain patterns: Contact

Bloodied object touches a surface

Blood stain patterns: Trail

Circular drops on a surface from an object

Define the area of intersection and convergence

1. The location of the blood source can be
determined by drawing lines from the
various blood droplets to the point where
they intersect.
2. The area of convergence is the point of
origin—the spot where the “blow” occurred

What are secreters

Secretes are individuals whos blood type antigens are found in high concentration i their body fluids, such as saliva, semen, and gastric juices