Read A Good Bloodstain Lately?
Since not all blood deposited at crime scenes is spatter, investigators now call this extremely valuable evidence, “bloodstain.” Detectives can learn a lot from studying bloodstain patterns, such as what type weapon was used to deliver the fatal blow, the manner in which the victim was killed, where the assault took place, and where the attacker stood when he committed the act. They learn these things by studying the shapes of the blood drops and droplets, the location of the blood evidence, the patterns made by the spatter and stain—generally, what happened to the blood when it was released from the victim.
A good bloodstain training class uses actual human blood, because nothing else accurately mimics the real stuff. Although, a decent substitute 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.
– 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
– 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 only measure bloodstains that hit surfaces on the way up, never 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 from changing the name from bloodspatter to bloodstain).
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.
*Images provided by HemoSpat.
This entry is both facinating and slighty morbid. Ah, the marvels of forensics…
Sarah – You mean the stuff they show on Castle isn’t accurate?
Jena – Thanks for the link. Good stuff. I was also glad to see the site mention Herb McDonnell, the “godfather” of bloodspatter. McDonnell sort of pioneered the study of bloodstain (spatter), and he trained many of the experts out there today. I, too, have used much of his information over the years.
If someone is looking for more on bloodstain pattern analysis, Joe Slemko has his tutorial online at http://bloodspatter.com/BPATutorial.htm
I took my Forensic Science course from Joe, who’s an officer in Edmonton Police Service and instructor at MacEwan College.
Love this post, Lee. Especially the photo of projected blood, since it never looks that way on television.
This is great stuff. The information provided by Lee never ceases to amaze me.
Hi Michelle –
Send me your address at my regular email and I will mail you a copy of CAIN when I get back to NYC. I would love for you to have a copy – and it’s the least I can do! xx
Great post, Alix! I’m still trying to get my hands on a copy of Mark of Cain, it sounds fascinating. And your book is remarkable, a must-read for anyone interested in crime and it’s larger impact.
What a fascinating look into an equally fascinating subject.
I have long beleived that if the human mind can conceive of it, someone will try to do it. That is why I am no longer shocked at the things people do to one another. Disgusted, perhaps, but not shocked.
That’s a great point you make about the same crime being different when depending on who is committing it and why. Thank you for taking the time to read this and comment. Your job sounds fascinating. Very best, Alix
Thanks for taking the time, Alix. Interesting subject. Crime can be as varied as the individual committing it. You can even say that the same crime committed by 2 different people for 2 different reasons is not really the same crime at all. I work in a job (for a forensic psychiatrist) that puts me in the fringe area of people who have committed crimes (ie, I don’t come in direct contact with them, but hear their stories). Lots of reasons pop up for the crime: mental illness, fear, desperation, greed, self-preservation, etc. And plain stupidity comes up, too.
Again, very interesting post.
I enjoyed your blog post immensely, Alix. Thanks Lee for posting a notice about this on the SEMWA list. I have been very interested lately in what makes villains tick.