Lisa Black, a guest of honor at the recent Killer Nashville conference, is not only the popular author of several crime series, she’s a certified crime scene analyst. She began her talk about blood stains by reminding us that blood accounts for about eight percent of a person’s body weight, about 5-6 liters for men and 4-5 liters for women. In real numbers, this is about 1.2 to 1.5 gallons. A lot to clean up.
If you’re writing about a crime scene and want to fling some blood around, these are the types of blood stains Black noted (here’s a good article for more detail and some pictures):
- Passive stains, or drips. A droplet’s size will depend in part on what kind of surface it dropped onto (absorbent or not) and how far the drop fell.
- Transfer stains—that is, swipes or wipes. People (or, conceivably, pets) get blood on themselves and transfer it from the place of origin to another surface—the bloody handprint by the door kind of thing. I once had a housepainter with a long ponytail, which was constantly getting in the newly painted surface. When he’d whip his head around, I got transfer stains on my furniture, woodwork, and everything else!
- Projected or impact stains—a bloodstain cause by arterial blood may show an up-and-down pattern due to the pumping of the heart; a castoff stain comes from swinging a bloody object, possibly the weapon, and can reveal information about the object as well as the number of strikes (the first strike is “free”—the weapon isn’t bloody yet); splash or drip patterns of a liquid dripping into another liquid; and the very fine droplets of high-velocity spatter.
As blood flies around your crime scene, the tail on the droplet tells investigators which direction it was traveling and, therefore, which direction it came from. Investigators painstakingly recreate in three dimensions the “area of convergence,” using the shapes and tails of all the drops to calculate angles. This may be a little hard to visualize (the best pictures I found appear to be copyrighted), but at this link, which is full of useful information, you’ll find an illustration of convergence under the heading “Examination of a bloody crime scene is a slow and methodical procedures.” Amen to that!
If your character doesn’t see any blood, never fear. There are tools to bring it into view. Amido black is a general protein stain that makes fingerprints, footprints, and other patterns visible. Anyone familiar with Gone Girl came to appreciate the magic of Luminol, which is specific to blood, and especially useful in detecting minute amounts after attempted clean-ups. It works through a reaction with the iron in hemoglobin.
One last tidbit from Black that might come in handy as you write: Bleach destroys DNA. Plus, as Oyinkan Braithwaite began her award-winning novel, My Sister, the Serial Killer: “I bet you didn’t know that bleach masks the smell of blood.”