Blood Analysis Quiz 2/11

How does the surface affect the shape of a blood droplet?

The surface the blood falls on will impact the shape of the blood droplet.

What shape does a blood droplet take on clean glass or plastic?

The droplet will have smooth outside edges and be round.

What happens to a blood droplet on a rough surface?

It will produce jagged edges (spines).

What occurs when blood hits a surface?

It will separate and form distinct patterns dependent on the velocity of the droplet.

What are satellite droplets?

Small droplets that form around the main droplet upon impact.

What are splines in blood spatter analysis?

Jagged edges that appear on blood droplets when they hit a rough surface.

What are tails in blood spatter analysis?

Tails are elongated shapes that form on droplets indicating the direction of travel.

Blood Spatter Types

Passive

Transfer

Projected

What is a characteristic of passive blood spatter?

These droplets will usually be uniform in size and shape.

What can the size of a blood droplet indicate?

The height from which the drop fell, how much blood was present, and the movement of the victim or assailant.

How can the height of a blood drop's fall be determined?

By examining the size and shape of passive drops of blood.

What does a larger diameter of a blood drop indicate?

The faster the drop moves, the higher it fell from.

What is the relationship between the diameter of a blood drop and height?

The diameter of the blood drop is consistent with the height up to 7 feet.

What happens to the diameter of a blood droplet after falling from a height of 7 feet?

The speed of the blood droplet does not increase, thus the diameter does not increase.

Blood Droplets or Blood Pool?

The size of the blood droplet can also tell us how much blood the victim potentially lost

Pools of blood may show flow patterns

These "streams" of blood will flow with gravity

The blood stream will follow natural contours if the surface it is following against and usually will end in a pool. This can tell us where someone was laying if the body has been moved or removed from the scene

What factors can determine the direction and speed of someone who is bleeding?

The size, shape, and distance between passive droplets.

How does the speed of movement affect the distance between blood droplets?

The faster someone is moving, the more distance there is between the droplets.

What may indicate the angle at which blood hits the floor?

There may be a tail on the droplet.

What are transfer patterns in blood evidence?

Transfer patterns happen when something or someone touches wet blood, then swipes, or touches another surface.

What surfaces can blood be transferred from?

Blood can be transferred from hands, shoes, clothing, and hair.

What can blood be transferred to?

Blood can be transferred to anything.

What type of image do blood transfers usually produce?

These transfers will usually produce a mirror image of the bloodied object.

What are the types of patterns that can be identified in blood transfer?

The pattern is usually identifiable as a wipe, swipe, or a transfer.

How can shoe prints be related to blood transfer evidence?

Investigators can potentially match a type of shoe to bloody footprints left at the scene.

Can fingerprints provide usable evidence in blood transfer cases?

Occasionally there is enough detail in a bloodied fingerprint to obtain usable evidence.

Wipe/Swipe Patterns

Blood patterns that show wipe or swipe type movements show that a bloody object (like, say, a dead body?) was dragged across a previously stained surface

This can give an indication as to if a body had previously been present at a crime scene and moved

What are projected blood patterns?

Projected blood patterns are the result of blood being moved by a force greater than gravity.

What can projected blood patterns indicate about the blood's movement?

They can indicate the direction the blood was moving and the movement of the victim or assailant.

What can projected blood patterns reveal about the origins of blood spatter?

They can reveal the origins of the blood spatter.

What information can projected blood patterns provide about the positions of individuals involved?

They can provide information about the position of the victim and assailant, the number of blows or shots, and the type of weapon used.

Low velocity Spatter

Low velocity is having a velocity of 5ft/s or less

It is usually greater than 4 mm in diameter

Blood movement due to a beating (with your fists or feet)

Medium Velocity Spatter

Medium velocity has a velocity of 5-25ft/s

The spatter size ranges between 1-4 mm in diameter

Examples include

blood resulting in blunt force trauma (hitting someone's head with a hammer)

Flicking blood off your hands or finger

High Velocity Spatter

High velocity spatter is defined as having a velocity of greater than 100 ft/s

It has a diameter of less than 1 mm

Examples include:

Gunshots

Explosions

Other high speed objects (like a propeller or high speed car crash

Arterial spray

What causes cast-off patterns?

Cast-off patterns are caused when an object is moved with enough force to throw droplets of blood off.

What happens to blood after the initial wound in relation to cast-off patterns?

After the initial wound, blood is transferred to the weapon and can be dispersed.

How can the direction of travel of a blood droplet be determined in cast-off patterns?

The direction of travel of the blood droplet can be determined by the tail that is created on impact.

What is a characteristic movement pattern that produces cast-off patterns?

Movements that produce cast-off patterns generally move in an arc.

What can drops of blood that appear to be dropped at a 90 degree angle indicate?

They can give an indication of where the assailant was standing during the attack.

What type of spatter occurs when a bullet enters the body?

Back spatter

What type of spatter occurs when a bullet exits the body?

Forwards spatter

What can spatter patterns indicate about a shooting incident?

The direction the bullet was traveling and the shooter's position

Arterial Spray

Formed when blood is forced out of an arterial wound due to the blood pressure

The pattern will usually show arcs that correlate with the heartbeat of the victim

What is the concept of blood leaving a 'tail' in the direction of movement?

It is an important concept when determining the point of convergence.

How many blood stains are needed to determine the point of convergence?

At least 2, preferably more.

What method can be used to determine the origin of blood spatter?

The 'string' method.

What tools can be used in the 'string' method to find the origin of blood spatter?

Imaginary lines or lasers.

What do you do with the lines in the 'string' method?

Determine where the lines overlap.

How to identify a blood stain:

There are several chemical tests that can be performed to determine if a stain left at a crime scene is actually blood or some other fluid

Blood testing reagent

Kastle-meyer color test

Leucomalachite green test

Takayama and teichmann tests

Blood testing reagent

The heme is hemoglobin, the oxygen carrying substance in blood cells, breaks down peroxides with the production of oxygen

Oxygen reacts with benzidine to turn it blue

Kastle-Meyer Color Test

This test is possible because of the catalytic breakdown of peroxides by hemoglobin

The phenolphthalein reagent and hydrogen peroxide mixed with the blood produces a pink color, proving blood has been found.

Differentiating between Human or Animal blood

The precipitin test uses animal serum containing antibodies specific to human antigens, causing human blood to clump

Serum is a liquid that separates from clotted blood

Can dried blood still be typed?

Yes, real blood that has been dried can still be typed because the red blood cells have ruptured, but the antigens and antibodies are still present.

How do investigators collect dried blood samples?

Investigators will collect the blood in paper bags to allow air to access the blood stain.

How is dried blood evaluated for blood type?

Cells are scraped from the sample and evaluated for blood type.

What can happen if moisture is trapped with dried blood?

Mold can begin to form on the blood.