A Gatineau couple found dead and decomposing in their apartment alongside an unharmed three-year-old died from an accidental fentanyl overdose, a coroner has found.

The bodies of 20-year-old Amélie Gauthier-Matte and 33-year-old Christopher Lecouvie were discovered in an advanced state of decomposition, their bodies lying intertwined on a bed at their rue ​Bégin home near Moussette Park on Monday, Feb. 27.

They're believed to have died four days earlier, on Thursday, Feb. 23, but weren't found until the child was noticed throwing toys out a window, according to coroner's reports released Thursday.

That prompted a neighbour and friend of the couple to check on them.

Drugs found in their systems

Gauthier-Matte and Lecouvie both had fentanyl, MDMA and methamphetamine in their systems, toxicology results showed. Gauthier-Matte also had heroin metabolites in her system, while Lecouvie showed cannabis in his, the reports said.

They died from respiratory failure caused by fentanyl intoxication, the coroner concluded.

Hakim Farhat, who regularly visits a friend in the same building, told CBC News in February he last saw the couple three or four days before they were found dead.

"They were in the balcony, I remember... I think they were with a couple of friends but nothing really like a hard party or anything. They were just talking or something. Sometimes I see them barbecue, sometimes I see them playing with the kid on the balcony, but I never expected such a thing to happen," Farhat said.

Neighbours said the couple had been living in the apartment for at least six months.