US police are investigating how Friends star Matthew Perry got the high dose of ketamine that was found in his body and determined to have caused his death.

The disclosure on Tuesday (local time) of an ongoing criminal probe by Los Angeles Police and two federal agencies came five months after the Los Angeles County medical examiner concluded Perry succumbed to an accidental overdose of the powerful prescription drug and drowning.

No foul play suspected is suspected in his death in October 2023.

The December 15 autopsy report concluded Perry died from the “acute effects of ketamine”, which combined with other factors caused the actor to lose consciousness and slip below the water in the hot tub at his Los Angeles home.

“Based on the medical examiner’s findings, the Los Angeles Police Department, with the assistance of the Drug Enforcement Administration and the US Postal Inspection Service, has continued its investigation into the circumstances of Mr Perry’s death,” the LAPD said.

A police spokesperson said detectives from the LAPD’s robbery-homicide division were conducting the police inquiry.

Toxicology tests found ketamine, a short-acting anaesthetic with hallucinogenic properties, in Perry’s body at dangerously high levels well within the range typically associated with general anaesthesia used in monitored surgical care, the autopsy said.

Coronary artery disease, the effects of the opioid-addiction medicine buprenorphine – also detected in his system – and drowning were listed as contributing factors in his October 28 death.

Perry, 54, who publicly acknowledged decades of drug and alcohol abuse, including the years he starred as Chandler Bing on the hit 1990s television sitcom Friends, had been sober for 19 months with no known relapses before his death, according to interviews cited in his autopsy.

Witness interviews in the report said he had been having ketamine infusion therapy for depression and anxiety.

His last known treatment was 10 days before his death, so the ketamine found in his system by medical examiners would have been introduced since that last infusion, the autopsy said.

“The exact method of intake in Mr Perry’s case is unknown,” the report said, adding that trace amounts of ketamine showed up in his stomach. No needle marks were found on his body, it said.

How the US actor might have obtained ketamine on his own or who might have supplied it to him were left open questions and, according to an LAPD spokesperson, are the focus of the ongoing investigation.

A DEA spokesperson declined to comment on the investigation, referring media inquiries to the LAPD.

Perry’s death shocked the world. His family confirmed the “tragic loss” in a statement, saying they were heartbroken.

A day later, his Friends co-stars Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matt LeBlanc and David Schwimmer issued a joint statement.

“We are all so utterly devastated by the loss of Matthew. We were more than just cast mates. We are a family. There is so much to say, but right now we’re going to take a moment to grieve and process this unfathomable loss,” they wrote.

“In time we will say more, as and when we are able. For now, our thoughts and our love are with Matty’s family, his friends, and everyone who loved him around the world.”

Perry was honoured during the in-memoriam segment at the BAFTA TV Awards ceremony earlier this month, and at the Emmy Awards in January.

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-with AAP