A new investigative technique based on Y-chromosome DNA and surnames has been adopted in a Quebec court for the first time. To solve Guylaine Potvin’s murder more than 20 years ago, authorities used DNA data available on the Internet, which allowed them to pinpoint the surname “Grenon,” a forensic biology expert explained.
Valérie Clermont-Beaudoin’s testimony was delivered Tuesday morning at the Chicoutimi court in the trial of Marc-André Grenon. A 49-year-old man, accused of sexual assault and murder, pleaded not guilty.
The specialist described in detail how her work provided the police with clues to the investigation: in particular, they used DNA data that her team found on the Internet and that was voluntarily provided by people who wanted create your family tree.
Wanted killer
A 19-year-old student was found murdered in her apartment in Jonquière on April 28, 2000. Her undressed body showed signs of violence. Biological fluids – containing DNA – were taken from the crime scene at the time, but he did not match any suspect known to police.
Then, in October 2022, the network came under fire: Grenon was arrested in Granby by investigators from the Disappearances and Unsolved Files Division of the Sûreté du Québec. How could they do it, all these years after the crimes were committed? At the time, police only mentioned “new investigative methods in forensic biology” without giving further details.
The 14 jurors in the criminal trial learned how this is possible on Tuesday.
Science in the service of justice
The forensic biologist’s testimony essentially consisted of explaining the last name search method by which she provided investigators with the last name “Grenon.”
First, she determined the genetic profile of the Y chromosome present in a sample taken from the crime scene, specifically under the fingernails of the victim’s right hand. This profile was then compared to the thousands of Y profiles present in the pYste database of the Quebec Forensic Sciences and Legal Medicine Laboratory (LSJML).
LSJML created pYste by consulting and collecting publicly available data on the Family Tree DNA website, which hosts approximately 100 genetic genealogy databases. These contain the genetic profile of the Y chromosome and the surname (paternal surname) of people who have voluntarily provided their DNA to one of the private organizations concerned in order to obtain information that will be used to compile their family tree.
“Since only males have the Y chromosome, it is passed from father to son only at conception, and thus from generation to generation, until the Y line is interrupted, either by adoption, sperm donation, or extramarital intercourse, which would mean that the father he will not be the biological father of his son,” explained the forensic expert from LSJML.
“In various cultures, including Quebec society, surnames and the Y chromosome are generally passed down in association from father to son for generations. Then, after determining the genetic profile of the Y chromosome, we could determine the surname that would be associated with it. »
The expert then used computer tools to search pYste for surnames associated with Y profiles that were closest to the unknown person’s surname. To do this, the computer compared about twenty specific locations (alleles) of the unknown Y chromosome with those on all Y chromosomes present in the database. Among the hundred thousand Y profiles present in pYste, two surnames stood out because of their close similarity to the foreign Y profile.
A perfect match
For the surname “Grenon”, the correspondence of the specific locations on the Y chromosome for which the DNA sequence was available appeared to be “perfect”.
Its score was 94, and the second-place surname – Verduzco – received 80.5.
This information was then passed on to investigators, who had amassed a list of hundreds of names of witnesses, suspects and persons of interest since 2000. There was that Marc-André Grenon.
However, the work of the police is not over. They still had to compare the DNA of the suspect’s entire genome (all his chromosomes) with the sample taken from the crime scene, underlined Mme Clermont-Beaudoin.
Odkal led them to the cinema where the suspect had gone: there they found a glass and two straws that Grenon threw away at the end of the film. DNA found on the straws was analyzed and matched DNA at the crime scene, investigators told the court. Grenon was then arrested and analysis subsequently confirmed the results: his DNA matched the DNA found on Guylaine Potvin’s body.
The judge warned the jury: the mere identification of the name “Grenon” cannot prove the man’s involvement in the crimes.
In cross-examination, Marc-André Grenon’s lawyers tried to demonstrate the shortcomings of this new method of forensic genealogy to confirm its unreliability. Their client is also presumed innocent until proven guilty.