Category Archives: Graduate School

Forensics on the Road

Last fall I took a course called Motor Vehicle Accident Investigation, and it was one of the most fun and informative classes of my grad school career. Every chance he got, our instructor took us out of the classroom to do actual field work. One such afternoon we conducted skid tests, in order to practice taking measurements and analyzing evidence.

In the video below, you can see what one such skid test looked like. Yes, that’s me in the passenger seat! It was a BLAST 🙂
What you should note is that my classmates are placing chalk marks at the beginning of the skid at what is called the “erasuremark” – it may seem like there is no skid where they are marking, but if you look closer you can see a faint outline of where the heat produced by the skidding tires hasn’t built up enough yet to lay down sufficient rubber. Measurements need to be taken starting with the beginning of the erasuremark.

In this next video, we explored what happens when a car skids with its wheels turned… (pay no attention to the noise in the background; we were at a police training facility so random gun shots and noise were to be expected)

NO, you cannot turn out of a skid when you’re on a dry road surface, so don’t believe anyone who says they can. And like my professor, Roger, states, note the difference in the appearance of the skid marks: it’s very hard to pick out any tread or marks from the ribs of the tires. All of this gives investigators clues to what happened.

There’s a lot that goes into this besides stretching a measuring tape and laying down evidence cards. There’s actual MATH involved. I hate math. But Roger made this really easy. Suppose you needed to figure out the speed of a vehicle involved in a crash using its skid marks. I will use the example from the skid test in video #1 above. There’s a formula: S (speed) = the square root of 30 (a constant) X “d” (distance in feet) X “f” (drag factor). Bear with me here… I promise it won’t be bad. To get the drag factor, we used an accelerometer in the test car. But it can be obtained mathematically as well (I will spare you the calculations). And what you can’t see in the video is the student with the radar gun sitting off-camera to obtain the speed of the vehicle. The skid measured 81.2 feet. The square root of 30×81.2x.57 (our drag factor) = 37 miles per hour. The radar speed obtained was 35 mph! Pretty close! So if we hadn’t had the radar gun we could have determined speed by basic math! Cool, huh? Yes, I’m a geek. There are also formulas for calculating time, distance, velocity at acceleration, velocity at deceleration, etc., etc. And if you’d like me to explain drag factor and the formula for determining it, I would be happy to. Just know that you are a bigger geek than me, and I think you’re great. 🙂

More vehicle accident forensics to come later.

The Science of Blood, Part I

Who knew science could be so much fun?? This past term one of my courses was Bloodstain Pattern Analysis. I know, I know – you’re asking, “There’s actually enough to this to make an entire course out of it?” and my answer is “Yes!” We used a textbook and everything!

There’s really enough information for more than one class, but one is all I got. In any case, I had no idea all of the things that this specialty can tell an analyst. Interesting? Definitely. Informative? Absolutely. Gruesome? Perhaps, but remember, as crime scene investigators, we are looking for anything that can tell us what happened. We are trying to recreate the scene – put the pieces of the puzzle together, so to speak. Everything from fingerprints to trace evidence to blood can speak volumes. So we’re looking at the blood not as some freakish special effect from a horror movie, but as a puzzle piece. However, if you have a weak stomach you may want to stop reading. Or just skip the pictures.

Forgive me for working in reverse here, but I’m playing catch-up because I let so much time lapse and didn’t post regularly when I should have. I’m going to start with what constituted as our final: a case study and a partial re-enactment of two actual crimes that my professor investigated when he was a homicide detective. They both involved bludgeoning cases; one where there was relatively little bloodstain evidence, and the other where the victim sustained over thirty blows to the head with a hammer and there was an overwhelming amount of blood on the scene, as you can imagine. We concentrated on the second case.

Here, the prime suspect was the victim’s husband. When he woke up in the hospital after having tried to commit suicide by swallowing anything he could get his hands on before the police showed up (including bleach) while his wife was bleeding to death on the floor, he claimed that it was self-defense: she had come at him with a pot of rice that had been cooking, as well as a knife, and he had several (very superficial) knife wounds on his chest “to prove she attacked him”. I guess she was pretty scary to merit all that head trauma… oops, I mean… our job as investigators is not to judge. Or assume. Just to collect and analyze facts. Ahem.

As a class we studied photos of the scene. They showed clearly that the attack was confined to the kitchen, and that the largest area of blood spatter was concentrated on the lower front of the dishwasher. The attack must have involved her being close to the ground. While we didn’t see pictures of his clothing, my professor explained that her blood was found on the back and even on the inside of the lower legs of his pants.

Next came the recreation. Could we effectively re-enact the crime in order to study the blood stains and what they may tell us? Well, we could sure try. Materials needed: dropcloths, painter suits, a hammer, foam core boards to prop against the wall, two heavy plaster “heads” called Splatter Heads (I’m not making this up, folks – see pic)

Spatter head base, bladder, weapon

with flat surfaces to hold “bladders” filled with sheep blood,and two guinea pigs, I mean students, to serve as the suspects. One of the heads was positioned a few feet away from the foam core on the wall. After being suited up and duct taped to protect clothing and body parts from flying blood drops, the first suspect was free to beat on the Spatter Head. We counted his blows… up to 40 of them… and then stood back to admire the damage. See pictures…

Spatter from 3 feet away from wall

Spatter on suspect

The spatter on the wall from Suspect No. 1 sure didn’t resemble the overwhelming amount of blood seen in the actual crime scene photos. There wasn’t nearly as much and the patterns were different. But taking into consideration that the actual victim was moving at the time, and that our Suspect No. 1 was not swinging with force (in an effort to save the classroom and himself from being covered in sheep’s blood) the resulting stains could be somewhat understandable. However, what should be noted is the back spatter on his clothing and just how much of the victim’s blood would be found on him – patterns can clearly be distinguished from the way he was kneeling and the way the clothing was bunched. But it was confined mostly to the front of him. The actual case suspect had blood droplets on the back (and inside) of his jeans. Why?

On to Suspect No. 2. In this case the Spatter Head was moved to within inches of the wall. And this “suspect” didn’t hold back. A softball player in “real life”, Kristen swung at the head with the force of a ball player in the last inning of the World Series. Her swings were much more extended and powerful, and the resulting spatter of thirty-some hits showed it.

Suspect No. 2; closer to the wall than Suspect No. 1

Much closer to the actual crime scene photos

Proud suspect

This looked MUCH closer to the actual crime scene, proving that at some point during the crime, the victim was on her knees inches from the dishwasher. The blows she sustained were powerful and strong. And unlike with Suspect No. 1, Kristen also had blood drops on her back – she was swinging wider and harder – the drops came from the hammer cast off backwards. In addition, the detectives at the actual scene determined that the blood on the inside of the suspect’s pant legs came from the fact that they had been rolled up at the time of the crime, exposing the inside fabric.

Studying the spatter closer, my professor pointed out areas within the overall staining that showed individual blows. We could also see areas that had a pinkish hue, called atomized blood or misting – which often results from what’s known as high-velocity impact spatter, seen frequently in gunshot cases. With high-velocity spatter, the size of preponderant stain is 1 mm or smaller, as opposed to low-velocity spatter, which involves stains greater than or equal to 4 mm in diameter. In this case the pinkish hue came not from high-velocity but from the repetition of spatter in the same area.

This was perhaps the most fun and informative “final exam” I’ve ever taken – minus the clean up of course, which involved mopping floors and wiping down walls while the suspects went to the bathroom to wash the blood off their faces. Anyone seen the movie Sunshine Cleaning??? I will revisit Bloodstain Analysis again in the future since there’s so much to it and it’s just so damn cool. Now, how to apply this to animal cases? Same concepts, just different subjects, who bleed slower than humans and may have different spatter patterns as a result, plus they have lots of hair… hmm.. plenty of research for me.

And how did the actual case turn out? Well, the husband was convicted of aggravated assault (yes, ridiculous, I know, but apparently the court testimony involved a long story and cultural differences and the cooking consistency of rice… bunch of hooey, really). The knife wounds on his chest? Self-inflicted. A good lesson not only about blood but about the effectiveness of good counsel.

Protected: Ethics and judgment

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