Bloodstain pattern analysis

method where investigators take their observations and the results of the evidence and investigation to evaluate a likely sequence of events 

Crime Scene Reconstruction

Crime-scene reconstruction relies on

medical examiners, criminalists, and law enforcement personnel to recover physical evidence and to sort out the events surrounding the occurrence of a crime

What is a laser beam used for

A laser beam is used to determine the search area for the position of a shooter who has fired a bullet through a window and wounded a victim.

The crime-scene investigator must remember that the **________________** of bloodstains and spatters may be useful for interpreting and reconstructing the events that produced the bleeding.

location, distribution, and appearance

Bloodstain pattern interpretation may uncover:

\-The direction from which blood originated

\-The angle at which a blood droplet struck a surface

\-The location or position of a victim at the time a bloody wound was inflicted

\-The movement of a bleeding individual at the crime scene

\-The approximate number of blows that struck a bleeding victim

\-The approximate location of an individual delivering blows that produced a bloodstain pattern

What can provide valuable insights into the events that occurred during the commission of a violent crime when deposited on floors, walls, and bedding

Bloodstain patterns

What must be considered when determining a bloodstain direction, dropping distance, and angle of impact

Surface texture, the stain's shape, size, and location

True or False: In general, the harder and less porous the surface, the less spatter results

True

How can the direction of travel of blood striking an object be discerned?

The pointed end of a bloodstain always faces its direction of travel

How can the impact of blood on a flat surface be determined?

By measuring the degree of circular distortion

True or False: At a right angle the blood drop is circular

True

True or False: As the angle decreases, the stain becomes shorter

False (elongated)

Equation for Angle of Impact

arcsin(W/L)

Occurs when an object impacts a source of blood

Impact spatter

Projected outward and away from the source (when a projectile creates an exit wound)

Forward spatter

Also known as blow-back spatter, is projected backward from the source (when a projectile creates an entrance wound)

Back spatter

Area of convergence

The point on a two-dimensional plane from which the drops in an impact pattern originated

How can an area of convergence be established?

By drawing straight lines through the long axis of several individual bloodstains

Area of origin

The area in a three-dimensional space from which the blood was projected

What will the area of origin show?

The position of the victim or suspect

String method

Commonly used at a crime scene to approximate the position of the area of origin using found angles of impact of individual stains in the pattern

Fine forward sparred from an exit wound and back spatter from an entrance wound

Gunshot spatter

If the bullet does not exit the body, the gunshot wound only produces...?

Back spatter

Some back spatter may strike the shooter and enter the gun muzzle

Drawback effect

Created when a blood-covered object flings blood in an arc onto a nearby surface

Cast-off pattern

What is a cast-off pattern commonly produced by?

A bloody fist or weapon between delivering blows

The features of the cast-off pattern are affected by...?

Size of the object, the amount of blood, and the direction the object was moving

Projected pattern

Caused by an injury to the heart or a main artery and the pressure of the continued pumpin

The site of the initial injury to the artery can be found where the pattern begins with...?

The biggest spurt

True or False: The oxygenated blood spurting from the artery tends to be a brighter red color than blood expelled from impact wounds

True

Created by blood that is expelled from the mouth or nose from an internal injury

Expiration pattern

What can differentiate a pattern created by expirated blood?

Presence of bubbles of oxygen or a lighter color

Created when an object blocks the deposition of blood spatter onto a target surface or object, and the spatter is deposited onto the object or person instead

Void pattern

What may give a clue as to the size and shape of the missing object or person?

The blank space

Created when an object with blood on it touches one that does not have blood on it

Contact/transfer pattern

Produced when the object contacts the surface and is removed without any movement of the object

Simple transfer patters

May be caused by movement of the bloody object across a surface

Wipe patterns

Made by drops or large amounts of blood flowing by the pull of gravity

flow patterns

True or False: The flow direction may show movements of objects or bodies while the flow was still in progress or after the blood dried

True

Interruption of a flow pattern

may indicate the sequence and passage of time between the flow and its interruption

Occurs when blood collects in a level (not sloped) and undisturbed place

Pool of blood

True or False: The edges of a pool of blood dry first

True

Occurs when the edges of a stain dry to the surface; it is also called skeletonization

Perimeter stains

Perimeter stains occurs within how many seconds of deposition of droplets?

50 seconds

True or False: It takes a shorter amount of time for larger volumes of blood to make perimeter stains

False (longer)

Knowing the skeletonization time allows an investigator to determine the...?

Timing of movement or activity