Forensics (5th Period)

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"Good afternoon, everyone. Please turn in your homework by the end of class."

"Today, we're going to begin examining the use of blood spatter analysis. Anyone with a weak stomach needs to take a seat next to a garbage can."

She passes around a series of photographs.

There are hundreds of methods and analytical techniques used in the forensic laboratory. While many of these methods are common biological, immunological, biochemical, or microscopic tests used in scientific research, others are unique to the forensic field. Forensic analysis is not only concerned with recognizing and identifying unknown substances, it is also actively used in the complete reconstruction of crime scene events and conditions.

One technique used by crime scene investigators is the analysis of stains left by blood shed at a scene. Bloodstain pattern analysis is a powerful forensic tool used in crime scene investigations. If the investigator understands the dynamics of an altercation, how blood be haves when it exits the body, and how it reacts when it contacts a surface, then an attempt can be made to understand what happened and to determine if a crime occurred. The trained forensic scientist looks at the patterns made by shed blood and tries to determine what did and/or did not happen. Interpreting the bloodstain patterns involves physical measurement of blood droplets, pattern recognition using known photographs or experiments, the use of trigonometry, and knowledge of the physics of motion.

Together with other types of evidence from the crime scene (such as fingerprints, tool mark and footprint impressions, DNA evidence, chemical analysis, etc.) the forensic investigator pieces together the puzzle to re-create a logical sequence of events, which is supported by crime scene evidence. Collecting and documenting the evidence correctly is another skill just as important as interpreting evidence. Bloodstains cannot always be carried back to the lab, so care in documenting the scene is of utmost importance. Photographs and detailed sketches drawn to scale are invaluable tools that help piece together the puzzle.



"Learn the following set of terms and definitions -- there will be a quiz on Friday."

Angle of Impact: the angle at which a blood droplet strikes a surface

Arterial Gushing: the large pattern of blood that is created when blood escapes an artery under pressure; the increase and decrease in blood pressure is apparent

Arterial Spurts: large patterns created under pressure, but with less volume and usually more distinctive evidence of blood pressure rising and falling

Clot: a mass of blood and other contaminants caused through clotting mechanisms

Cast-Off Stains: blood that has been thrown from a secondary object (weapon or hand) onto a target other than the impact site

Drop Patterns: characteristic patterns present when blood drips into standing, wet blood

Expiratory Blood: blood which is spattered onto a target, as a result of breathing; typically, this occurs when an injury is sustained to the throat, mouth, or airway

Impact Site: usually the point on the body that received the blow or applied force, from which the blood was shed

Origin: the point in space where the blood spatter came from

Parent Drop: the droplet from which satellite spatter originated

Projected Blood: blood under pressure that strikes a target

Satellite Spatters: small drops of blood that break off from the parent spatter when the parent droplet strikes a target surface

Shadowing/Ghosting/Void: a pattern that helps to place an object or body in the scene; normally, the area in question lacks blood even though areas surrounding it show blood

Skeletonized Stain: the pattern left when an object moves through a partially dried stain, removing part of the blood, but leaving the outline of the stain intact

Spatter: bloodstains created from the application of force or energy to the area where the blood is

Spines: the pointed edges of a stain that radiate out to form the spatter

Splash: pattern created when a volume of blood in excess of 1 mL strikes a surface at a low to medium velocity

Swipe: the transfer of blood onto a target surface by a bloody object that is usually moving laterally

Transfer Pattern: the pattern created when a wet, bloody object comes in contact with a target surface, leaving a pattern that has the features of the object making it useful for identifying the object

Target: the surface where the blood ends up

Wipe: pattern created when a secondary target moves through an existing wet blood stain on some other object

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