When Friends actor Matthew Perry was found dead in a hot tub at his Los Angeles home last year, it seemed like it could have just been an accident.

He’d been treating his depression with ketamine infusion therapy, wasn’t found with drug paraphernalia or anything suggesting foul play, and appeared to have drowned.

He’d spent decades fighting addiction, but the actor had said he was finally clean.

As the world mourned the passing of the actor, known for playing Chandler Bing on Friends, a coroner found something curious: high levels of ketamine in his blood, in the range used for general anaesthesia during surgery.

It should not have still been in his system since his last therapy appointment more than a week prior.

According to US prosecutors, a nearly year-long investigation that followed uncovered an alleged vast underground ketamine dealing network, cover-up attempts and another death.

It led to five arrests – including medical doctors, Perry’s assistant and an alleged dealer they said was known locally as the “Ketamine Queen”.

His live-in assistant, Kenneth Iwamasa, pleaded guilty to one count of conspiring to distribute ketamine causing death, and two other people – Eric Fleming and Dr Mark Chavez – also pleaded guilty to conspiring to distribute drugs unlawfully.

Dr Salvador Plasencia, accused of supplying ketamine to Perry, is charged with falsifying records. Alleged dealer Jasveen Sangha faces nine counts, including conspiracy to distribute ketamine and distribution of ketamine resulting in death.

Both pleaded not guilty in court on Thursday.

Ms Sangha’s name comes up again and again in the investigation.

Authorities allege the “Ketamine Queen” supplied the drugs that led to Perry’s death on 28 October 2023.

The 41-year-old is accused of selling 50 vials of ketamine to him for about $11,000 (£8,550) and is described by prosecutors as a drug trafficker who knew the ketamine she distributed could be deadly.

Her North Hollywood home was a “drug-selling emporium”, Martin Estrada, the US attorney for California’s Central District, told a news conference.

More than 80 vials of ketamine were allegedly found there in a search, along with thousands of pills that included methamphetamine, cocaine and Xanax.

A handgun was also discovered, Mr Estrada said.

The home, called the “Sangha Stash House” in the indictment, was where she is alleged to have packaged and distributed drugs, mostly for the rich and famous.

Ms Sangha “only deal[s] with high end and celebs”, according to the indictment.

Before the news conference ended, Mr Estrada was asked about the scale of Ms Sangha’s alleged network.

He alleged she was a “major source of supply for ketamine to others as well as Perry”.

As Perry fell deeper into addiction, he wanted more and more ketamine and sought it for lower prices, which led to him to street dealers as well as the more elite providers, authorities said.

Those charged in the case took advantage of him, Mr Estrada said.

“I wonder how much this moron will pay?” Dr Plasencia wrote in one text message, according to authorities.

In another, he said he wanted to be Perry’s “go-to for drugs”.

It is alleged that Perry paid them around $2,000 for vials that actually cost about $12 a piece.

“These defendants cared more about profiting off of Mr Perry than caring for his well-being,” said Mr Estrada.

Authorities say Perry purchased 20 vials of ketamine from Dr Plasencia for a total of $55,000 between September and October 2023.

Dr Plasencia also allegedly taught Iwamasa, the assistant, how to inject the drug, even though he had learned “that Perry’s ketamine addiction was spiralling out of control”, according to investigators.

Authorities say the doctor provided more ketamine even though he witnessed Perry “freeze up” while administering the drug on one occasion.

Following Perry’s death, those accused of supplying him with the drugs attempted to hide their actions, investigators say.

Authorities say Ms Sangha sent a message to another suspect telling him to “delete all our messages”.

Fleming is alleged to have messaged Ms Sangha: “Please call… Got more info and want to bounce ideas off you. I’m 90% sure everyone is protected. I never dealt with [Perry] only his assistant. So the assistant was the enabler.”

He also asked Ms Sangha, according to court documents, whether ketamine stay “in your system or is it immediately flushed out”.

Authorities say they used coded language, calling ketamine “Dr Pepper”, “bots” or “cans”.

Dr Plasencia allegedly falsified medical records in an attempt to make the drugs given to the actor look legitimate.

Authorities also uncovered that Ms Sangha was allegedly tied to another overdose death in 2019.

According to court documents, she knew about the dangers of ketamine after selling it to a customer named Cody McLaury, who died of an overdose after buying the drug.

One of his family members is said to have texted her saying: “The ketamine you sold my brother killed him. It’s listed as the cause of death.”

Days later, investigators say, Ms Sangha searched on Google: “Can ketamine be listed as a cause of death?”

Authorities say Ms Sangha will face charges in that case.

Perry’s live-in assistant, Iwamasa, was the person who found the actor dead.

Investigators say he was also the one who injected Perry with the ketamine that led to his death.

Iwamasa never received medical training and “knew little, if anything” about administering controlled substances, according to court documents.

In the four days leading up to and including Perry’s death, prosecutors say Iwamasa administered more than 20 shots of ketamine, three on the day the actor died.

He was charged in July with one count of conspiracy to distribute ketamine resulting in death and serious bodily injury. Prosecutors say he has since pled guilty to the charge.

Ketamine is supposed to be administered only by a physician, investigators say, and patients who have taken the drug should be monitored by a professional because of its possible harmful effects.

On 10 October, weeks before Perry’s death, Dr Plasencia is alleged to have bought 10 vials of ketamine from accused co-conspirator Dr Mark Chavez, which he intended to sell to Perry.

Authorities say Dr Plasencia then met Perry and Iwamasa in a public parking lot, where the doctor injected the actor while inside a vehicle.

Two days later, he allegedly injected him at home with a large dose that caused him to “freeze up” and his blood pressure to spike.

Dr Plasencia told Iwamasa something to the effect of, “Let’s not do that again.”

But he allegedly left additional vials with Iwamasa.

Perry was open about his addictions. His 2022 memoir described decades struggling with alcohol and drugs. He wrote about his co-star Jennifer Anniston confronting him over smelling alcohol on his breath and the millions he’d spent trying to remain sober.

He said that he hoped his openness would help others who were struggling. The homepage for the Matthew Perry Foundation, set up after his death, has his quote: “When I die, I want helping others to be the first thing that’s mentioned.”

The head of the federal Drug Enforcement Agency, Anne Milgram, said on Thursday that the arrests and the public details of the high-profile case were likely to help others and prevent deaths – exactly as Perry had wanted.