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 a contributing factor in his death.

Los Angeles Police Capt. Scot Williams said in an email Tuesday that the police department was working with the Drug Enforcement Agency and 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. The investigation was first reported by TMZ.

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. The drug is sometimes used to treat depression.

The Los Angeles County Department of Medical Examiner said in the autopsy report that Perry also drowned in “the heated end of his pool,” but that it was a secondary factor in his death, deemed an accident.

According to Perry’s autopsy, people close to the actor told investigators that he was undergoing ketamine infusion therapy, an experimental treatment used to treat depression and anxiety. But the medical examiner said that his last treatment 1 1/2 weeks earlier wouldn’t explain the levels of ketamine in Perry’s blood. The drug is typically metabolized in a matter of hours.

Perry was among the biggest television stars of his generation when he played Chandler Bing alongside Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matt LeBlanc and David Schwimmer for 10 seasons from 1994 to 2004 on NBC’s megahit sitcom “Friends.”

The Associated Press