Lexington, Virginia • August 19, 2010
When the impeccably punctual Dr. Greenstone, professor of geology, didn't show up for class one day, her students notified campus security at Washington and Lee University. An officer drove to her house to investigate. He found the professor at the bottom of the cellar stairs--dead from a broken neck.
That's the scenario of the fictional crime that Fred LaRiviere, assistant professor of chemistry at W&L, asks his students to solve in his course Biochemistry Lab II, a requirement for all biochemistry majors.
The twist? Students must use DNA samples from dogs to solve the crime.
LaRiviere said that 40 percent of U.S. households contain at least one dog; thus, many crime scenes contain traces of canine residue such as hair. Simulations of burglary and assault have shown that contamination by animal hairs is virtually certain when a criminal enters the home of a pet owner.
LaRiviere added that dog DNA has certain characteristics that have not been found in humans or, as far as he is aware, in cats. Dogs are also an easy source of samples, since there is an abundance of dog owners in W&L's chemistry and biology departments, including LaRiviere's own dog, Casper.
Back at the fictional crime scene, Dr. Greenstone's body yields a collection of dog hairs, unusual for a woman who disliked animals. But the DNA scientist at the Virginia State Crime Laboratory is out sick, so W&L's students have been asked to assist in the case.
The crime is complicated and has multiple suspects-a student disgruntled about failing Greenstone's course, a faculty member who blames Greenstone for his being denied tenure, and Greenstone's sister, the lone beneficiary of her large life insurance policy.
Each suspect either owns a dog or lives with one.
To make things more difficult, two of the suspects' dogs are not only of the same breed but also from the same breeder (Lexington being a small town). Sometimes, depending on the dog samples he has, LaRiviere makes the two dogs siblings with similar DNA profiles. "That forces the students to look at all of the data to figure it out," he said.
The students' assignment is to extract the DNA from the dog hairs and create a DNA profile for each piece of canine evidence associated with the crime. They must test each sample twice to get some idea of reproducibility. They then analyze the resulting data using a polymerase chain reaction in a thermal cycler. Finally, they produce a written report that could reasonably be used as expert evidence in court.
"Sometimes the answer is not entirely obvious," said LaRiviere. "It depends on how well the students have worked up the samples. But that's all part of the exercise. The students may think a particular dog matches best with the crime scene, but they also need to consider whether that is enough to convict the person."
LaRiviere created the lab experiment with Julie Millard, a biochemist at Colby College. They wanted to find out whether a crime scenario would be an exciting hook for presenting laboratory techniques to students. They both asked their students to "solve" the crime, and then examined the resulting data about the students' experiences, which they published in the Journal of Chemical Education in 2009.
The study found that the motivation to finger the culprit brought an excitement to such experiments that often surpassed exercises with a predictable outcome. In fact, students at W&L have responded so positively to LaRiviere's innovative experiment that he plans to develop a spring term course on forensic science for non-majors in the next few years.