CanCon 2015 day 2: Blood spatter pattern analysis

Presenter: Detective Constable Garneau of the Ottawa Police

Note: The Constable introduced himself, explained what his job entails, and the education he needed to do his job. He told us that he hadn’t presented to writers before and that he’s brought along the material that he’d present to an introductory forensics class. Then he told us that he spoke to a writer about what would be important for a writer to know. He was advised to focus on the physical evidence and on the interpretation of that evidence through case studies. We wouldn’t need to know the history of forensic science or much about the physics.

So, he asked us if we would mind terribly if he focused on that material. He also warned us, even though it was in the program, that he would be presenting some graphic material. He was so polite.


Blood spatter pattern analysis tells the examiner:

  • The direction the blood droplet was travelling;
  • The angle of impact;
  • The mechanism(s) that contributed to the creation of the pattern;
  • The area of origin;
  • The minimum number of impacts for any source of blood;
  • The relative positions of person(s) or object(s) involved;
  • The sequence of event(s); and
  • The identity of the perpetrator.

The most useful evidence is the outliers.

I confirm theories using science. I don’t work for the Crown, or the defence. I work for the court.

Blood behaves according to the principles of physics. It will behave differently, and look differently, on different surfaces.

In lab simulations, I use sheep’s blood, but then I would also have to explain how sheep’s blood behaves similarly to human blood when I present the evidence in court. If I don’t have to use a lot of blood for the simulation, I’ll use my own.

There are three kinds of blood spatter patterns:

  1. Passive;
  2. Spatter; and
  3. Transfers.

Passive blood spatter patterns are affected by gravity and include: drip stain patterns, drip trail patterns, drip patterns, splash patterns, pool patterns, saturation, and flow patterns.

Spatters are caused by a physical action and include: mist patterns, expiration patterns, cast-off patterns, cessation cast-off patterns, projected (e.g. arterial spray) patterns, and impact patterns. Impact patterns are the fun ones. I have to use physics and math to explain them.

Transfers occur when a blood-covered object touches another object, leaving a pattern behind. Transfer patterns include: the transfer stain, the swipe pattern, and the wipe pattern.

Many of us develop morbid senses of humour. It’s a way to protect ourselves from the impact of all the horrible things we see every day.

For impact patterns, we now have software which will map everything out based on our measurements. I could use strings, and in some cases, I have to, but it’s very time-consuming. Dexter does it wrong, by the way. You can be very precise.

I use trigonometry to determine the area of origin/impact.

The rest of the presentation was specific case studies and how the Constable’s blood spatter pattern analysis resulted in a resolution to the crime. In some cases, it was a positive outcome. In some, it was not. Most of the crimes presented were perpetrated by men against women, often their girlfriends, or spouses.

It was gruesome, but fascinating.

Next week: Getting noticed (in a good way) 🙂

Be with the one you love, tomorrow.

Phil and I will be heading to an afternoon movie (Deadpool!) and dinner.