Toronto police say that a drug squad officer who passed away in April died of a fentanyl overdose.

Const. Michael Thompson was found in him home in medical distress, according to police, and died three days later.

Investigators say the quantity of fentanyl found in his body was too large to have been caused by mere contact with the drug.

Police say Thompson had regular access to street-level drugs as a drug squad officer.

"It is always a difficult time when we lose a member of the Toronto Police Service, regardless of the circumstances," acting chief Jim Ramer says in a statement. "It's even more difficult when the circumstances of a specific loss leave us with more questions than answers."

The 37-year-old officer was hired by the Toronto Police Service in 2006, and had worked with the drug squad since December 2014.

Toronto police spokesperson Meaghan Gray says their investigation of the circumstances surrounding Thompson's death has not revealed at this point how he got the drugs.

"Yes, it's a possibility that those drugs were taken from the drug squad," Gray says. "It's also a possibility that they were obtained at the street level. We simply don't know at this point and it's quite possible we may never know."

She says the service has tightened the rules surrounding the handling of evidence, but will not reveal what those changes are.

When asked why it took so long to release this information to the public, Gray says the cause of death wasn't known until July when Toronto police launched an internal investigation.

"It wasn't until very recently that we felt we had enough information."

The circumstances surrounding his death could lead to some of the cases he worked on being tossed. A number of cases will be back in court on Monday, when Crown prosecutors are expected to make changes to how the cases proceed, or not, through the justice system.