Ch 4 Bloodstain Pattern Analysis

Characteristics of Liquid blood

-Specific gravity

-Viscosity

-Surface Tension

Surface Tension

Is a characteristic of liquids whereby they are resistant to penetration or separation. The surface acts to reduce surface area. A small mass of liquid which becomes detached becomes rounded into a sphere; the shape gives the minimum service area for any given volume; a falling blood drop is not tear-drop shaped.

Blood flowing downwards towards the fingertips from a cut on the hand

-Accumulates on the fingertip and increases in volume until the gravitational pull (its weight) exceeds surface tension

- Such droplets will have a fairly uniform volume of 0.05 ml

More rapid bleeding may

-Result in slightly larger drops

Slower Bleeding

-Does not result in smaller drops

-Moving source ( smaller droplets)

Terminal Velocity

-Of the falling blood drop depends on its size.

Smaller drops

Have a lower terminal velocity and acquire it after a shorter fall distance

Larger Drops

Accelerate over a greater distance and therefore attain a greater terminal velocity.

Size of the Bloodstain

-Depends more on the nature of the target surface than the distance fallen

-Vary only slightly with increasing fall distance

-Little change in fall distance above seven feet

Shape of the blood spot

-Depends mostly on the texture of the target surface

-Blood landing on smooth glass will be consistent and uniform in shape ( circular )

-Blood landing on textured surfaces such as paper and wood will be of variable shape & will have irregular edge characteristics

Angled Impact: Vertical drops onto tilted target

-Blood striking a smooth surface at 90 degrees results in an approximately circular blood stain.

-As the angle of impact becomes a more oblique the blood stain becomes more elongated and its length to width ratio increases.

Impact of Angel

-arc sin (width of stain/ length of stain)

-Accurate measurement of the blood stain is required

Point Of Convergence

Drawing lines along long axis of several stains will show a point of convergence at their origin.

Point of origin

-Lies at a point in space above the point of convergence

-Measurement of impact angle allows translation of 2-D image (convergence) into 3-D (origin).

-At a crime scene, strings, tapes and protractors are commonly used.

-Computer programs are also utilized

Impact Spatter

Bloodstain pattern produced when an object makes forceful contact with a source of blood, projecting drops of blood outward from the source."

Blood spatter patterns are classified according to the ?

Velocity with which the blood is struck

Low-Velocity blood spatter

-Blood source subjected to a low velocity impact (less than 5 ft per second) e.g. free-falling blood under the influence of gravity

-Examples: blood cast off from fist, shoe, weapon, dripping, splashing

-Blood spots of this type are mostly 4 mm or greater in diameter

Medium Velocity blood spatter

-Blood source subjected to a medium velocity impact (about 5 to 25 ft/s)

-Examples: blows with a baseball bat, hammer, axe or similar instrument

-Blood spots typically from about 1 to 4 mm in diameter

High Velocity blood spatter

-Blood source subjected to a high velocity impact (100 ft/s or greater)

-Examples: gunshot; high velocity machinery; explosion

-Blood spots typically less than 1 mm in diameter (a fine mist)

In gunshot related cases?

-Back spatter

-Forward spatter

Back Spatter

Results from blood being blown back from entry wound towards the firer and weapon

Forward Spatter

Results when blood exits the wound and passes in the same direction as the projectile

Dripped Blood

When blood drips into itself, many small droplets are projected upwards into the air and impact around the central irregular blood pool at in the right angles and obliquely, resulting in surrounding circular and oval blood spatter patterns.

Splashed Blood

-Blood volumes exceeding 1 ml, traveling at a velocity of less than 5 ft per second or subjected to a minor impact, squirted, thrown against a vertical surface, or stomped.

-Results in an irregular central splashing pattern, surrounded by directional elongated blood spots.

Arterial Spurting

-Characteristic bloodstain pattern containing spurts due to blood exiting under pressure from an arterial injury.

-Wave form and associated flow patterns may be evident because of the spurting and large volume of blood associated with this type of injury.

Wipe Patterns

Object moves through a wet bloodstain. Feathered edge suggests directionality.

Transfer Pattern

-Wet, bloodied object contacts a secondary surface

-Transfer from hand, fingers, shoes, weapon, and hair

-Transfer to walls, ceilings, clothing, and bedding

-Produces mirror-image of bloodied object

Flow Pattern

-Blood flows horizontally & vertically, altered by contours, obstacles; often ends in a pool.

-Pooled blood on absorbent surfaces may be absorbed and diffused which can create a pattern larger than the original pool.

Void Pattern

"An area within a deposited spatter pattern that is clear of spatter, caused by an object or person blocking the area at the time of the spatter's deposition

_______ is the method used to support a likely sequence of events at a crime scene by the observation and evaluation of physical evidence and statements made by individuals involved with the incident.

Crime-scene reconstruction

Reconstructing the circumstances of a crime scene is a team effort that may include the help of law enforcement personnel, medical examiners, and ________.

Criminalist

Violent contact between individuals at a crime scene frequently produces bleeding and results in the formation of ________.

Blood stain patterns

The proper interpretation of bloodstain patterns necessitates carefully planned ________ using surface materials comparable to those found at the crime scene.

Control Experiment

Bloodstain patterns may convey to the analyst the location and movements of ___ or ___ during the commission of a crime.

Victim/ Assailant

True or False: Harder and less porous surfaces result in less spatter, whereas rough surfaces result in stains with more spatter and serrated edges.

True

Generally, bloodstain diameter (increases, decreases) with height.

Increase

The ___ and ____ of blood striking an object may be discerned by the stain's shape.

-Direction of travel

-Angel of Impact

A drop of blood that strikes a surface at an angle of impact of approximately 90 degrees will be close to (elliptical, circular) in shape.

Circular

The angle of impact of an individual bloodstain cab be estimated using the ratio of ___ divided by ____.

-Width

-Length

______ is the most common type of blood spatter found at a crime scene and is produced when an object forcefully contacts a source of blood.

Impact Spatter

Forward spatter consists of the blood projected backward from the source, and back spatter is projected outward and away from the source.

False

The classification system of impact spatter is based on the size of drops resulting from the velocity of the blood drops produced, and patterns can be classified as ______, _______, or_______ impact spatter.

-Low

-Medium

-High Velocity

True or False: The velocity classification system is a good way to classify impact patterns and to determine the kind of force that produced them.

True

The ______ is the point on a two-dimensional plane from which the drops originated.

Area of coveragence

The _____ of a bloodstain pattern in s three-dimensional space illustrates the position of the victim or suspect when the stain-producing event took place.

Area of origin

The _____ method is used at the crime scene to determine the area of origin.

String

A ______ is created by contact between a bloody object and a surface.

Transfer Pattern

Movement of a bloody object across a surface, (lightens, darkens) as the pattern moves away from the point of contact.

Lightens

True or False: Footwear transfer patterns created by an individual who was running typically show imprints with more space between them compared to those of an individual who was walking.

True

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

True

The approximate drying time of a __________ of blood determined by experimentation is related to the environmental condition of the scene and may suggest how much time has elapsed since its deposition.

Pool

The edges of a bloodstain generally ______ within 50 seconds of deposition and are left intact even if the central area of a bloodstain is altered by a wiping motion.

Skeletonize

A ____ pattern commonly originates from repeated strikes from weapons or fists and is characterized by an arc pattern of separate drops showing directionality.

Cast-off

True or False: Characteristics of a cast-off pattern arc cannot give clues as to the kind of object that was used to produce the pattern.

False

When an injury is suffered to an artery, the pressure of the continuing pumping of blood projects blood out of the injured area in spurts creating a pattern known as _______.

Arterial Spray

If a ______ pattern is found at a scene, it may show movement, lead to a discarded weapon, or provide identification of the suspect by his or her own blood.

Drip Trail

A bloodstain pattern created by ______ features bubbles of oxygen in the drying drops and may be lighter of oxygen in the drying drops and may be lighter in color when compared to impact spatter.

Expirated blood pattern

The shape and size of the blank space, or ______. created when an object blocks the deposition of spatter onto a surface and is then removed may give a clue as to the size and shape of the missing object or person.

Void

True or False :Each bloodstain pattern found at a crime scene should be noted, studied and photographed.

True

When documenting bloodstain patterns, the ______ involves setting up a grid of squares known dimensions over the entire pattern and taking overview, medium-range, and close-up photographs with and without the grid.

Grid Method

The ___ method of bloodstain documentation involves setting up a border of rulers around the pattern and then placing a small ruler next to each stain to show relative position and size in photographs.

Perimeter Ruler

True or False : The pointed end of a bloodstain always faces toward the direction of travel.

True