Common Terminology for Advancing the Science of Forensics
By Don Ostermeyer
Northwestern Center for Public Safety bloodstain instructors have collaborated on developing a working vocabulary for bloodstain pattern analysts and other professionals in the field. In order to limit misinterpretation or confusion, it is critical that analysts use consistent terminology, whether speaking to jurors in a courtroom, communicating with other law enforcement and public safety professionals, or discussing industry topics with each other.
The glossary of terms that the NUCPS bloodstain instructors have authored does not attempt to re-invent the wheel but focuses on the simple, understandable, and common vocabulary that is essential to the development of an industrywide vocabulary. Whether you are a seasoned bloodstain expert or a student, a new detective, or a criminal defense attorney or prosecutor, the following glossary comprises the recommended terminology for testimony and reconstruction in the area of Bloodstain Pattern Analysis. The terminology also is incorporated into the new NUCPS Forensic Bloodstain Investigator Certification Program and the Bloodstain Evidence courses.
Glossary of Terms
Blood
- Stain – The discoloration of a target surface penetrated by blood providing for the basis for study.
- Drop – Blood volume of approximately 0.5ml, falling or dropping to a surface.
- Parent Drop / Parent Stain – The droplet or stain from which the satellite spatter occurred.
- Clot – A mass of blood and other contaminates caused through the clotting mechanism.
Blood Pattern
Note: Blood patterns always originate below the angle of incidence.
- Drip – Blood volume of 0.1ml or greater, falling one drop at a time from a fixed location and most often due to inertia (lack of circulation).
- Splashed – Blood volume of 0.1ml or greater, spilling / falling at least 4” or being subjected to minor impact prior to striking a surface. A splash pattern is sometimes referred to as “low velocity.”
- Projected – Blood propelling outward in some manner, faster than normal gravitational speed. The resultant stain pattern is commonly attributed to arterial gushing or spurting. Projected patterns may also be related to coughing, vomiting, or purging of blood. Blood may also be projected when a blood pool is forcefully impacted by some object.
Cast-Off
- Cast-off – Blood that is “flung” or “cast” from an object at a termination of motion. A cast-off pattern appears as a linear or arc-like series of droplets becoming increasingly elongated in their direction of travel.
- Cast-off Triangulationn – A cast-off pattern may be triangulated back to the area of the object at the moment of termination of the motion of swing. Cast-off patterns are associate with weapons used in blunt force trauma. Triangulation of cast-off patterns may locate the perpetrator when the wounds were inflicted.
- Spines – The pointed edges of stain that radiate out from the spatter.
Convergence – The point or site where a conical mass of droplets is tracked back to a common location.
Flow
- Directional – A series of blood drops in motion when landing horizontally or cascading vertically onto a surface. The tails and spatter point the direction of travel.
- Stationary – A series of blood drops landing vertically onto a surface cascading in a linear fashion with little or no directionality.
- Terminal – A series of blood drops that are abruptly terminated due to limited blood supply or inertia. This action may also be referred to as “passive.”
Point of Origin – The calculated point where an incident of forceful bloodshed occurred.
Predominate – A dominant characteristic or factor of greater influence. Predominate is applied to spatter droplets as a function of the degree of force.
Shadowing / Ghosting / Void – A break or absence in a pattern due to the presence of an intermediate or intervening object.
Spatter
- Spatter – Small droplets resulting from disruption of whole blood drop onto substrates.
- Satellite – Small droplets surrounding a blood pool resulting from rupture due to characteristics of a landing surface. Satellite spatter is observed to branch out in a radial direction from a common nucleus.
- Medium impactt – Conically projected blood mass created by forces of 25 feet per second or less and commonly attributed to blunt force trauma.
- High impact – Conically projected blood mass created by forces of 100’ per second and more and commonly associated with gunshot trauma. The predominant size of spatter stains related to high force is 1mm and less.
- Atomized Mist – A conical mist-like mass present in a forward-spatter pattern characteristic for a gunshot.
- Ricochet – Stains that have impacted some other objects and fallen to the target.
Transfer
- Transfer – A pattern that is created when liquid or drying blood is transferred in some fashion from one surface to another.
- Secondary – A transfer pattern created when blood flows from one surface and transfers to another surface.
- Contact Swipe – A transfer pattern produced when an object stained with blood moves across a surface.
- Contact Wipe – A stained surface in the drying process moves across a surface.
- Compression – Transfer patterns that appear blanched in the center mass due to the weight of an object present during blood flow.
- Impression – A mirror image of an object stained with blood after contact with a surface.
- Repetitive – Multiple impression images, similar in appearance, that diminish in their direction of travel.