LOS ANGELES (AP) — An investigation has been opened into the death of Matthew Perry and how the “Friends” actor received the anesthetic ketamine, which was ruled contributing factor in his death.

Los Angeles Police Capt. Scot Williams says Tuesday that the police department was working with the Drug Enforcement Administration and the U.S. Postal Inspection Service with a probe into why the 54-year-old star had so much ketamine in his system when he died in October.

Perry was found unresponsive in the hot tub of his Los Angeles home.

His autopsy released in December found that the amount of ketamine in Perry’s blood was in the range used for general anesthesia during surgery.