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Trish Hennessey and Nash Campbell died in a vehicle fire in St. Felix in western P.E.I. on June 21. (Hennessey Cutcliffe Funeral Home)

Police on Prince Edward Island have ruled that the vehicle fire that claimed the life of Patricia Hennessey and her four-year-old son in June was a homicide-suicide.

Autopsy results show Hennessey, 37, and Nash Campbell, 4, had prescription drugs in their systems when they died of smoke inhalation on Martin Road in St. Felix, near Tignish.

Police released the autopsy and toxicology results on Wednesday.

Investigators said the fire was not mechanical and there's no evidence anyone else was involved.

"You know we know and I think it's just common sense that a four year old is not going to take prescription drugs on his own," said Sgt. Andrew Blackadar.

"At this point I'm willing to say that there was no mechanical failure at all in the vehicle. It was a deliberately set fire in the vehicle.

Firefighters found the bodies in the charred vehicle on June 21 around 1 a.m.

Sources have confirmed to CBC that Hennessey lost custody of her son the day before.

Their bodies were found just hours before the boy was to be turned over to his father Marc Campbell.

CBC and the Charlottetown Guardian have applied to the courts for access to records related to this case.

Blackadar said families on both sides are devastated.

He said the RCMP investigation is now complete.