This is a first in Quebec: a new scientific investigation technique based on the DNA of the Y chromosome was presented in a criminal trial, after being used by the police to solve the murder of a student committed more than 20 years ago in Jonquière.
The surname “Grenon”, that of the man accused of the murder of Guylaine Potvin, was identified using DNA data available on the Internet, and matched that found at the crime scene, detailed in courtroom an expert in forensic biology.
The testimony of Valérie Clermont Beaudoin was given Tuesday morning at the criminal trial of Marc-André Grenon, 49, which is taking place at the Chicoutimi courthouse.
She revealed that her work gave the police investigative leads, in particular by using DNA data that her team found on the Internet, and which had been provided voluntarily by people wishing to establish their family tree.
A wanted murderer
For more than 20 years, the murderer of Guylaine Potvin was at large.
The 19-year-old student was found murdered in her apartment in Jonquière on April 28, 2000. Her undressed body showed signs of violence and sexual assault. Biological fluids – containing DNA – were taken at the time from the crime scene, but the profile of the attacker was then unknown to investigators.
Then, in October 2022, a dragnet: Grenon was arrested in Granby by investigators from the Disappearances and Unresolved Files Division of the Sûreté du Québec (SQ). How did they do it, all these years after the crimes committed? At that time, the police simply mentioned “new investigative methods in forensic biology”, without further details.
The 14 jurors at the trial learned Tuesday how this was possible.
Science at the service of Justice
The testimony of the specialist in forensic biology essentially consisted of explaining the method of searching for surnames that she used to provide investigators with the surname “Grenon”. This method first consisted of establishing the genetic profile of the Y chromosome present in the sample taken from the crime scene, more precisely under the nails of the victim’s right hand. This profile was then compared to the thousands of Y profiles present in the pYste database of the Laboratory of Judicial Sciences and Legal Medicine of Quebec (LSJML).
The LSJML formed pYste by consulting and collecting data on the Family Tree DNA website which hosts around a hundred genetic genealogy databases. These databases contain the genetic profile of the Y chromosome and the surname (paternal family name) of people who voluntarily provided their DNA to these private organizations in order to obtain information to build their family tree.
“The Y chromosome, which determines the biological sex of men, is transmitted from the father to his sons, from generation to generation, unless there is a breakage due to adoption, sperm donation or an extramarital conception,” clarified the LSJML forensic science expert. And “as in Quebec society, in general, the family name follows the same transmission as the Y chromosome, we can determine a family name from a Y profile.”
The expert then used computer tools to search in pYste for the surnames associated with the Y profiles which were closest to that of the unknown person. To do this, the computer compared around twenty particular sites on the Y chromosome of the unknown to those of all the Y chromosomes present in the pYste database. Among the hundred thousand Y profiles present in pYste, two surnames stood out because of their close resemblance to the stranger’s Y profile. For the surname Grenon, the correspondence at the specific sites of the chromosome for which the DNA sequence was available appeared perfect.
This name was then passed on to investigators.
Their work was not finished. To confirm the identity of the potential suspect discovered by the surname search, it was necessary to compare the DNA of his entire genome (all his chromosomes) to that of the sample taken from the crime scene, underlined Mme Clermont Beaudoin.
The police then continued their efforts and their eyes were directed more specifically towards Marc-André Grenon, who now lived in Granby. A surveillance and a police operation led them to a cinema where Grenon went. The police recovered a glass and two straws which he threw away after the film. The DNA found on the straws was analyzed and matched that found at the crime scene, investigators told the trial. Grenon was then arrested.
In cross-examination, Marc-André Grenon’s lawyers attempted to demonstrate the flaws of the biological method, raising various elements to argue that it is unreliable.
The trial will continue Wednesday morning with the continuation of the cross-examination of the expert.