Murder of Guylaine Potvin | A cup and two straws led to the arrest of the accused

A cup and two straws: 22 years after the murder of Guylaine Potvin, a major scientific breakthrough allowed the police to begin tracking and recover these few items which ultimately betrayed the man now accused of the crime.

This was explained by the Crown prosecutor, Mr.^e Pierre-Alexandre Bernard, during his opening statement, on the second day of the trial of Marc-André Grenon, which opened this week at the Chicoutimi courthouse, in Saguenay-Lac-Saint-Jean.

The 49-year-old man is accused of having sexually assaulted and killed Guylaine Potvin on April 28, 2000, at her apartment in Jonquière, Saguenay. He has pleaded not guilty to both charges.

Alerted by a friend who had found the body of the young woman in the morning, the police quickly concluded that there was a “suspicious presence” on the scene, reported M^e Bernard.

Since “a crime scene means a lot,” a forensic identification technician is called to the scene. A belt and a box of condoms were seized on site. A “biological analysis” of these items will allow us to conclude that there is another individual on the scene, a man.

“But the DNA profile alone does not formally identify someone. It takes a comparison,” described M^e Bernard, addressing the jurors.

However, there are no direct witnesses to the crime. Several avenues are explored, but the investigation stalls. “The file remains open. Several suspects will be eliminated from the list of suspects, little by little, but it is clear that the days, months, years pass without us being able to match the DNA found on the scene,” underlined Mr.^e Bernard.

Innovative technology

Until the entry on the scene, in June 2022, of the Laboratory of Forensic Sciences and Forensic Medicine. The government body, which brings together experts from several disciplines, is proposing to the investigators responsible for the file to add it to what is designated as the “PatronYme project”.

This recently developed technology focuses on the Y chromosome, a component of DNA that only men have. It then draws on large databases to associate a genetic profile with a last name.

“This chromosome comes to us from our father who received it from his own father. (…) From father to son, there is transmission of this chromosome,” detailed the Crown prosecutor. “Another thing also which, in customs, in Western social conventions, is transmitted from father to son: it is the family name. »

That of Marc-André Grenon then emerges and is judged to be “priority” in the investigation.

A spinning is authorized at its location, during which a cup and two straws will be recovered “legally”, took care to specify M^e Bernard.

The suspect’s DNA collected from these items is compared to that found at the Jonquière crime scene. It agrees.

With this information in mind, the police obtained a warrant to arrest Marc-André Grenon and take a DNA sample from him. Once again, the DNA matched that found on the belt and the condom box.

On October 22, 2022, Marc-André Grenon was arrested. Twenty-two years after the murder of Guylaine Potvin. “We sometimes say that justice advances slowly, but we also say that it has a long arm,” declared M in conclusion.^e Bernard.