Blood Spatter Analysis

Blood-spatter Pattern Analysis or

Bloodstain Pattern Interpretation(BPA/BPI)

• Reconstructing events that must have happened to produce bleeding

• Requires BPA specialist

Blood Pattern Reconstruction

Scene Pattern Reconstruction

1. Stain condition

2. Pattern

3. Distribution

4. Location

5. Directionality

Lab Results Reconstruction

1. Genetic marker typing

2. Age determination

3. Source determination

4. Race determination

5. Sex determination

—From Cracking Cases by Dr. Henry C. Lee and Thomas W. O’Neil

Blood Spatter Evidence

A field of forensic investigation that deals with the physical

properties of blood and the patterns produced under different

conditions as a result of various forces being applied to the

blood. Blood, as a fluid, follows the laws of physics.

Know Characterization of Bloodstains

1. Is it blood?

2. What species did it come from (human or animal)?

3. If it’s human, can it be associated with a particular individual?

People of Historical Significance

Paul Kirk (1902–1970) was a professor of criminalistics and biochemistry at the University of California at Berkeley. He actively assisted law enforcement organizations from 1935 to 1967. His book Crime Investigation contained a chapter in which he discussed the application of bloodstain pattern analysis to criminal investigations. Dr. Kirk analyzed the bloodstain pattern photos from the Sam Sheppard case and was instrumental in Sheppard’s release after his second trial. Find out more about the case at truTV’s Crime Library.

Blood Droplet Characteristics

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

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

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

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

Conditions Affecting Shape of Blood Droplet

Size of the droplet

Angle of impact

Velocity at which the blood droplet left its origin

Height

Texture of the target surface• On clean glass or plastic—droplet will have smooth outside edges• On a rough surface—will produce scalloping on the edges

Questions Answered by Blood Spatter Interpretation

The distance between the target surface and the origin of the blood

The point(s) of origin of the blood

Movement and direction of a person or an object

The number of blows, shots, etc., causing the bloodshed and/or the dispersal of blood

Type and direction of impact that produced the bloodshed

The position of the victim and/or object during bloodshed

Movement of the victim and/or object after bloodshed

Bloodstain Terminology

Angle of impact—angle at which blood strikes a target surface

Bloodstain transfer—when a bloody object comes into contact with a surface and leaves a patterned blood image on the surface

Backspatter—blood that is directed back toward the source of energy

Cast-off—blood that is thrown from an object in motion

Bloodstain Terminology, continued

Contact stain—bloodstains caused by contact between a wet blood-bearing surface and a second surface that may or may not have blood on it

• Transfer—an image is recognizable and may be identifiable with a particular object

• Swipe—wet blood is transferred to a surface that did not have blood on it

• Wipe—a non-blood-bearing object moves through a wet bloodstain, altering the appearance of the original stain

Bloodstain Terminology, continued

Directionality—relates to the direction a drop of blood travels in space from its point of origin

Terminal velocity—the greatest speed to which a free-falling drop of blood can accelerate in air. It is dependent upon the acceleration of gravity and the friction of the air against the blood—approximately 25.1 feet/second.

• High velocity—greater than 25 feet per second, usually 100 feet per second; gives a fine mist appearance

• Medium velocity—5 to 25 feet per second• Low velocity—5 feet per second or less

Bloodstain Patterns

The shape of a blood drop:

Round—if it falls straight down at a 90-degree angle

Elliptical—blood droplets elongate as the angle decreases from 90 to 0 degrees; the angle can be determined by the following formula:

Impact

The more acute the angle of impact, the more elongated the stain.

90-degree angles are perfectly round drops; 80-degree angles take on a more elliptical shape.

At about 30 degrees the stain will begin to produce a tail.

The more acute the angle, the easier it is to determine the direction of travel.

Bloodstain Patterns

The harder and less porous the surface, the less the blood drop will break apart.

The softer and more porous the surface, the more the blood drop will break apart.

The pointed end of the bloodstain faces the direction of travel.

Area of Intersection and Convergence

The location of the blood source can be determined by drawing lines from the various blood droplets to the point where they intersect.

The area of convergence is the point of origin—the spot where the “blow” occurred. It may be established at the scene by measurement of angles with the use of strings.

Blood Evidence

Class evidence for blood includes blood type. If you can determine the DNA, you will have individual evidence.

Bloodstain patterns are considered circumstantial evidence in a courtroom. Experts can argue many points, including direction of travel, height of the perpetrator, position of the victim, left/right hand, whether the body was moved, etc.

• Once it’s determined to be human, it must be protected as part of the crime scene

• BPA specialist will determine what POSITION and SHAPE indicate

• Measurements are taken to determine TRAJECTORY and DISTANCE– Controlled experiments– Uses surface materials similar to those at the

scene

Herbert Leon MacDonell

• Leading authority on bloodstain interpretation• Tips for investigators

• “It is possible to determine the impact angle of blood on a flat surface by measuring the degree of circular distortion of the stain. In other words, the shape of the stain tends to change depending upon the angle of impact, which caused the stain. For example, the more the angle decreases, the more the stain is less circular and longer.”

• “Surface texture is one of the key components in determining spatter type.”

• Harder surface=less spatter• Important to duplicate surface in a

controlled test

• “When a droplet hits the surface, which is hard as well as smooth, the blood actually breaks apart upon impact. This in turn creates smaller droplets. The smaller droplets will continue to move in the same direction as the original droplet.”

• Smaller the size of spatter=greater energy required to produce spatter

• Low, Medium, and high velocity impact spatter may be identified by representative sizes (but exceptions must also be considered)

• Diameter of large blood spatter will be of little or no value in estimating the distance a drop of blood has fallen prior to impact.

• When considering the shape of a blood stain for use in calculating its angle of impact, only a sharp, well-defined blood stain should be used for measuring its width and length

• Directionality of a blood drop while in flight is usually obvious from the geometry of its resulting blood stain– The pointed end indicates direction of travel of

the drop prior to impact on a surface– Direction of travel may also be determined

when edge scallops only appear on one side of the stain

• Before a drop of blood can fall, absent of any form of applied energy, gravitational attraction acting on blood drop must exceed its surface tension

• Surface texture of material on which blood falls onto MUST be taken into consideration in BPA

• Edge characteristics of drop have no value in establishing distance a drop may have fallen prior to impacting a surface unless the nature of the surface is considered

• Surface tension prevents spattering– Regardless of distance a drop has fallen before

impacting a smooth, hard surface such as glass

• A few blood stains do not make a pattern• Draw conclusions with reservations and/or

qualifications• It is ok to admit that there is insufficient

evidence to draw a conclusion from BPA• No opinion is better than an incorrect,

forced opinion

• When a dozen or more small bloodstains are present in a recognizable pattern, their size may allow for prediction as to the energy that was required to produce them

• When the preponderance of individual bloodstain diameters are less than 1mm, they are consistent with having been produced as the result of high velocity impact (most often shooting)

• When the preponderance of individual bloodstains are 1mm or more in diameter, they are consistent with having been produced as the result of medium velocity impact (most often beating or stabbing)

• The shape of a bloodstain is a function of the angle at which it hits/impacts the surface

• Perfectly roundninety-degree impact/drop angle

• Angle of impact of elliptical drop may be determined using length to width ratio of the drop

• Blood stains may be lifted of the surface of which they have impacted– The smoother and harder the surface is, the

easier it is to lift the stain

• When measurements and angles are used to establish the origin or origins in space, not only will the actual origin be somewhere below the point or points of convergence, but it must be remembered that the investigator is determining a specific area and not a small point of origin

• Sobriety of the victim will have NO significant effect on how the blood stain patterns are produced

• High blood alcohol level is of no concern to the interpretation of bloodstain patterns

• When blood is projected upward with sufficient force to strike a ceiling, it will almost always be a result of a gunshot having an upward trajectory– Such a trajectory is more often the result of a

suicide rather than a homicide

TO SOLVE A BLOODSTAIN'S ANGLE OF IMPACT10 mm Width / 20 mm Length = 0.5 = SIN of the AngleARC SIN of 0.5 = 30The Angle of Impact is 30o