LOS ANGELES (AP) Authorities have opened an investigation into how Matthew Perry received the supply of ketamine that killed him, police said Tuesday.

Los Angeles police are working with the U.S. Drug Enforcement Administration and the U.S. Postal Inspection Service with a probe into why the 54-year-old Friends star had so much of the drug in his system, LAPD Capt. Scot Williams said in an email.

An assistant found the 54-year-old Perry face down in his hot tub on Oct. 28, and paramedics who were called immediately declared him dead.

His autopsy, released in December, found that the amount of ketamine in his blood was in the range used for general anesthesia during surgery. It was listed as the primary cause of death, which was ruled an accident with no foul play suspected, the report said.

Drowning and other medical issues were contributing factors, the coroner said.

The investigation was first reported by TMZ.