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Introduction to Blood Spatter Analysis

Background

An explosion in media coverage of real crimes, as well as fictitious crime scenes depicted in television dramas has fueled a vast increase in public interest in forensic science techniques. Popular television shows and detective novels often depict the forensic scientist as a sort of jack of all trades, solving crimes and capturing criminals. In reality, these activities fall under the job description of the detectives in charge of the crime. The work of forensic scientists is broken down into several highly specialized subsets. Crime labs have several departments, each having their own staff of highly trained specialists that help analyze and examine each piece of evidence that is collected at the crime scene. Full service crime labs have the capability to examine blood, DNA, firearms, tool marks, drugs, alcohol, handwriting, documents, photography, video footage from the crime scene, trace evidence, and more. Each of these involves specific techniques requiring a great deal of expertise. In addition, most labs also employ several crime scene specialists that are called to the actual scene of the crime. These specialists are trained to secure and closely examine the crime scene for evidence that may elude the police officers handling the scene. The following chart shows a small portion of the specialty areas required to investigate specific types of evidence:

Type of Evidence

Area of Specialty

Blood groups

Serologist

Body tissue

Pathologist

DNA/RNA

Molecular Biologist

X-rays

Radiologist

Dentition and dental work

Odontologist

Insects

Entomologist

Plants

Botanist/phycologist

Soil

Microbiologist

Algae and other microbes

Geologist

Climatic conditions

Meteorologist

Age of remains and racial characteristics

Physical anthropologist

Hair and fibers

Microscopist

Personality disorders

Psychiatrist

Paint and glass fragments

Chemist

Drugs and poisons

Toxicologist

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.

Using this kit, you will be introduced to the basics of bloodstain pat tern analysis. It is in no way a comprehensive course that would be used to train a forensic investigator. The experiments will ask you to produce typical bloodstain patterns commonly found at a crime scene where blood has been shed. You will then sketch and document the patterns produced in each activity. Photographs are recommended so that a visual record can be kept. If this is not possible, attention to de tail in sketches is imperative. It is recommended that each group complete a notebook. Activity sheets, data, sketches, notes, and photos can be included in the notebook, as well as any assessments.

Mathematical skills needed for the activities involve taking metric measurements, using a caliper to measure small distances.

Glossary of Key Bloodstain Pattern Analysis Terms

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

OBJECTIVES