A good bloodstain training class typically uses actual blood, because nothing else accurately mimics the real stuff. Although, a decent substitute for the real deal is a mixture of Karo syrup and red food coloring.
During training classes students are exposed to nearly every type real-life scenario imaginable, but the first order of business is to learn the basics—characteristics of a blood drop.
Characteristics of a blood drop
– blood drops are formed by gravity
– blood drops cannot break apart unless contacted by an outside force
– larger drops travel further than smaller drops (due to mass, not size)
– blood drops always travel in an arcing path (impact injuries)
– size ranges from a few millimeters to few centimeters
– volume of a drop of blood is in direct proportion to whatever it’s dropping from (ax, stick, arm, leg, etc)
Crime scene investigators typically measure bloodstains that hit surfaces on the way up, not stains made by blood that’s on its way back down. Stains made when traveling upward are much more accurate for use as evidence because gravity is not as much of a factor in the pattern’s formation.
Types of Bloodstain Patterns
Impact – caused by high-velocity or medium-velocity wounds—gun shots or blows by an object such as a baseball bat or hammer.
Swipes (Wipes)– Caused by a bloody object being wiped across another surface. These stains are the reason for changing the name of the examination from “blood spatter” evidence to “bloodstain” evidence (not all patterns are caused by airborne drops of blood). Remember that in your writing. Patterns caused by spattering, splattering, or wiped-on blood is no longer called “blood spatter.”
Therefore, your characters should reflect the change, as have their real-life counterparts. An example of the change:
Detective Sergeant Catchemall studied the bloodstain pattern on and next to the ticking cow clock hanging on the kitchen wall. He stood there, staring, for what seemed like an eternity before turning toward his partner, Ridley Perkins. Then he tipped his bald, oval-shaped head back toward “the cow wall” where reddish splotches and dots of once-oozing blood contrasted sharply against the freshly painted, snow white surface. The cow’s tail moved from side to side with each tick-tock of the timepiece.
Tick Tock …
“I believe, Ridley,” he said, “that our killer was right-handed, shorter than your own meager five-and-a-half feet, and was standing, not sitting, quite close to our victim, poor Mrs. Ima Ghostnow, when he pulled the trigger on what was most likely a revolver. That, my friend, is what I believe happened to our unfortunate victim.”
Tick Tock …
*Terminology could vary from one area to the next.
Cast-Off– Caused by slinging blood off objects in motion (a swing of a bloody hammer, or arm).
Drip and Flow– Caused when blood drops off one object onto another.
Projected– Caused by arterial spurts. Often seen in stabbings and cuttings.
The ability to effectively interpret bloodstain patterns is a science and an art. But, before investigators can dive into a crime scene, they must learn a bit of terminology, such as:
Angle of Impact– the angle formed between the direction of an individual drop of blood and the surface it strikes.
Back Spatter– blood that’s directed back towards the source of energy, such as a hand holding a firearm, or hammer.
Expirated blood – blood that’s forced from the mouth or nose where air (exhalation) is the propellant.
High Velocity Impact Spatter (HVIS)– bloodstain pattern caused by a high velocity impact, such as those caused by gunshots or fast moving equipment or machinery (saws, drills, etc.)
Point of Convergence – the point (two dimensional) where the direction of travel (blood droplets) intersect. Can be used to help determine where the victim was standing when the fatal injury was delivered.
Point of Origin –the point (three dimensional) where the direction of travel (blood droplets) intersect.
Stringing – a method used to determine the point of origin. Investigators tie strings at the blood drops, following the direction of travel. The point where the strings intersect is the point of origin. Lasers are sometimes used in lieu of strings.
Stringing You Along!
The 2018 Writers’ Police academy offers a fantastic workshop on bloodstain pattern investigations. The class is taught by expert RJ Beam.
Remember, the Writers’ Police Academy is a hands-on training event for writers, readers, fans, and anyone who simply wants to learn more about police, firefighting, EMS, and forensics. Spots are open so click the link above and sign up today to attend this THRILLING event. See you there!