Blood spatter forensics test 3

What is the primary role of a forensic scientist in blood stain interpretation?

To use physical evidence of blood and blood stain patterns to describe what happened at a crime scene.

What can blood and blood stains indicate at a crime scene?

Who was present, when the crime occurred, positions and movements of individuals, and the type of weapon used.

What is impact spatter?

The most common type of bloodstain pattern that occurs when an object impacts a source of blood, consisting of droplets radiating from the origin.

What is the difference between forward spatter and back spatter?

Forward spatter is projected outward from a source (e.g., exit wound), while back spatter is projected backward from the source (e.g., entry wound).

What creates cast-off spatter?

When a blood-covered object flings blood in an arc onto a nearby surface, often seen when a person strikes someone with a weapon.

What is arterial spray?

Blood spurted from an injury to a main artery or the heart, caused by the pressure of the pumping blood.

What are void patterns?

Patterns created when an object blocks the deposition of blood spatter onto a target surface.

What is a transfer pattern?

Created when a surface carrying wet blood comes in contact with a second surface, such as footprints left in blood.

What are pools in blood stain analysis?

Areas where blood collects in a level and undisturbed place; if absorbed, it is called saturation.

What is a drip trail pattern?

Formed by the dripping of blood off a moving surface or person, often seen as passive drops.

What does a wipe pattern indicate?

Occurs when a dry object moves through pre-existing blood, with feathering indicating the direction of the wipe.

How can directionality of blood stains be determined?

By analyzing the tail of the bloodstain; the tail indicates the direction of travel.

What is the significance of the absence of a tail in blood drops?

It indicates that the blood dropped from a 90° angle, known as a passive drop.

What is the method used to determine the area of convergence for blood spatter?

Stringing is used to find the area of convergence, which helps determine the point of origin.

What is blood spatter analysis (BPA)?

The use of various shapes, sizes, and patterns of blood stains to reconstruct the events that caused bleeding.

What forces affect the shape of a blood droplet?

Gravity, cohesion, and adhesion.

What is cohesion in the context of blood droplets?

The attraction between blood molecules that causes droplets to stick together and form a spherical shape.

What is adhesion in blood droplet analysis?

The attraction between blood and unlike substances, causing spines or extensions on porous surfaces.

What is the terminal velocity of a free-falling drop of blood?

Around 25 feet per second, where it falls at a constant speed due to air resistance.

What is forensic serology?

A branch of forensic science that deals with the identification and analysis of bodily fluids found at crime scenes.

What tests can be used to determine if a stain is blood?

Benzidine Test, Kastle-Meyer Test, Hemastix, Luminol Test, Bluestar.

What is the purpose of blood typing in forensic investigations?

To eliminate suspects or confirm that blood does not match a victim; it is less time-consuming than DNA profiling.

What is the ABO blood group system?

A classification of blood based on the presence or absence of specific antigens on red blood cells.

Who discovered the ABO blood group system?

Karl Landsteiner, an Austrian immunologist, in the early 20th century.

What are the four major blood types in the ABO system?

A, B, AB, and O.

What is the Rh factor?

A protein found on red blood cells; if present, the blood type is Rh+; if absent, it is Rh-.

How many possible blood types exist when considering the Rh factor?

Eight possible blood types: A+, A-, B+, B-, AB+, AB-, O+, and O-.

What type of blood cell carries the proteins that determine blood type?

Red Blood Cells!

Name the three proteins that may be found in a blood sample that determine blood type.

A protein, B protein, D (Rh) protein

Name the blood type proteins found in a person’s blood who is O-

O- blood type has none of the blood type proteins!

A bloody handprint on the wall. What type of bloodstain pattern is this?

Transfer Pattern

Something smeared through blood on the floor. What type of bloodstain pattern is this?

Wipe Pattern

Is cast off blood pattern an example of high, medium, or low velocity blood spatter?

Cast off is Medium Velocity

What is cast off, how is it produced?

When a person is attacked with a weapon, blood will cover the weapon and fling off of it, creating a trail of blood for each swing.

Name two things we can learn from studying cast off patterns at a crime scene.

The approximate number of blows a victim received, approximate location in the room during the attack, approximate size of the weapon used

Blood type is ________ Evidence!

Class!

You want to know if B protein is present in a blood sample. Describe how you would find out.

Add anti-B serum to the sample. If the blood clumps, the protein is present.

What is the purpose of a Presumptive Test?

To determine if a stain is blood or not blood. (could be animal blood!)

What is the purpose of chemical treatments such as Luminol, Fluorescein, and Leuco Crystal Black?

These chemicals are applied to find latent blood stains (stains that cannot be seen with the eye)

Describe Low Velocity blood patterns, how are they formed?

Drops or pools of blood, formed when blood falls due to gravity (no force applied) also known as Passive blood stains

Describe the appearance of High Velocity spatter. What usually causes it?

Blood drops are very small, a mist of blood, usually caused by gunshot

Describe Medium Velocity spatter patterns. How are they formed?

Medium Velocity patterns are drops that are flung with force against a surface (wall, floor, ceiling, etc). Drops may come directly from a victim during an attack (drops fan out from central location), or fling off of the weapon (trail/line of blood drops).

What are ‘spines’ on a blood drop? What condition would cause drops to form many spines?

Spines radiate out from a blood drop, when it falls - more spines if it falls from a greater distance, more spines when it falls on a hard surface.

What are ‘satellites’ in a spatter pattern? What condition would cause drops to form many satellites?

Satellites are tiny drops of blood that spring out of the main drop due to force of impact. Dropping from greater distance, and especially dropping into a pool of blood.

As the angle of impact for a blood drop becomes smaller, the shape of the drop…

As the angle decreases the drop becomes more elongated

You have measured the angle of five different drops in the corner walls of a room. Describe how to use this information to determine where the victim was standing.

Extend lines out from each drop (using lasers or string) at the calculated angle. The lines will cross at the approximate location of the victim when attacked.