A small detail in a photograph led police in Saskatoon to Cheyenne Rose Antoine, who has pleaded guilty to the murder of Brittney Gargol

Police in the Canadian city of Saskatoon say a selfie posted on Facebook was instrumental in solving a murder investigation that spanned nearly two years.

Cheyenne Rose Antoine, 21, pleaded guilty this week to killing Brittney Gargol, who was found fatally injured on a road in the outskirts of the city in 2015. It was later determined that she had been strangled to death.

A belt was found lying next to her body. Police later noticed that Antoine was wearing an identical belt in a selfie that had been snapped hours before Gargol was found. The small detail – barely noticeable in a photo that showed the close friends smiling as they stood side by side – turned Antoine into a key suspect in the case.

Using the pair’s posts on social media, police were able to reconstruct a timeline of their night. “It’s quite remarkable how the police developed this information,” Robin Ritter, the crown prosecutor for the case told the Canadian Broadcasting Corporation.

A tip ultimately led police to a witness who said that Antoine had confessed to the killing soon after it happened. The woman said Antoine had showed up at her house in hysterics. She confessed that the two had argued after going to a house party and that she had hit Gargol and strangled her.

Antoine’s defence team told the court that the pair were drunk and high on marijuana when the argument took place. While she accepted responsibility for her friend’s death, Antoine did not remember killing her friend, her lawyer told the court.

Antoine was initially charged with second-degree murder, but pleaded guilty to manslaughter.

Her lawyer noted that Antoine had suffered years of physical and sexual abuse in the province’s foster care system. Antoine’s parents, both survivors of Canada’s residential school system, struggled with addictions issues.

In a statement, Antoine said she remained deeply affected by what had happened. “I will never forgive myself. Nothing I say or do will ever bring her back. I am very, very sorry … It shouldn’t have ever happened,” she said.