Kenneth Iwamasa “repeatedly” injected Perry with ketamine including on the day he died, federal authorities said.

Federal prosecutors revealed that Matthew Perry’s personal assistant administered the dose of ketamine that ultimately led to the Friends star’s death at age 54.

On Thursday, Aug. 15, federal authorities made the bombshell announcement that five people including Kenneth Iwamasa, 59, have been charged in connection with the actor’s death.

But how culpable is Iwamasa?

PEOPLE spoke to two legal experts about Iwamasa’s role in Perry’s Oct. 28, 2023 death, when the actor was found floating face-down in the hot tub at his Pacific Palisades home. One expert says the live-in assistant is the “least culpable” of the five people charged. Another, however, says Iwamasa is “the most closely tied to what eventually happened.”

An autopsy released in December showed that Perry died from acute effects of ketamine, in addition to other contributing factors such as drowning, coronary artery disease and effects from buprenorphine, a medication used to treat opioid use disorder. At the time of his death, Perry was undergoing ketamine infusion therapy, the autopsy found.

The nature of his death was determined to be “accidental,” according to the autopsy report.

The US Department of Justice announced on Thursday, Aug. 15, that Jasveen Sangha, 41, allegedly known as “The Ketamine Queen,” and Dr. Salvador Plascencia, 42, a licensed physician, are the lead defendants in the case.

Sangha allegedly “sold the batch” of ketamine that led to Perry’s death, U.S. Attorney E. Martin Estrada said at a press conference on Aug. 15.

Plascencia allegedly told another patient in mid-2023 that Perry “was spiraling out of control with his addiction” and yet he continued to offer ketamine to him, Estrada claimed at the press conference.

During one injection, “he saw Mr. Perry freeze up and his blood pressure spike,” Estrada said. “Despite that he left additional vials for defendant Iwamasa to administer to Mr. Perry.”

Erik Fleming, 54, pleaded guilty on Aug. 8 to one count of conspiracy to distribute ketamine and one count of distribution of ketamine resulting in death. He admitted in court documents that he distributed the ketamine that killed Perry, the U.S. Attorney said in a release.

Dr. Mark Chavez, 54, of San Diego, agreed to plead guilty to one count of conspiracy to distribute ketamine. He admitted in his plea agreement to allegedly selling the drug to Plasencia, the U.S. Attorney said in the release.

During a press conference on Aug. 15, Estrada said that the investigation into Perry’s death found that he “fell back into addiction” last fall.

Authorities allege that Iwamasa conspired with Sangha, Fleming and Plasencia, to illegally obtain ketamine and distribute it to Perry, the U.S. Attorney said in the release.

Iwamasa pleaded guilty on Aug. 7 to one count of conspiracy to distribute ketamine causing death.

Iwamasa “admitted to repeatedly injecting Perry with ketamine without medical training, including multiple injections on Perry on the day he died,” the U.S. Attorney says in the release.

Of those charged, Iwamasa is “the least culpable in my opinion,” Neama Rahmani, a former federal prosecutor and president of West Coast Trial Lawyers tells PEOPLE.

“I don’t think he is in the business of dealing drugs,” he speculated. “I think he’s in the business of being an assistant.”

Iwamasa had been Perry’s assistant since 1994 and lived with him. On the day Perry died, he administered three doses of ketamine to him, first at 8:30 a.m., and again at 12:30 p.m., according to Iwamasa’s plea agreement. Then, 40 minutes after that, Perry asked Iwamasa to get the hot tub ready for him, saying, “Shoot me up with a big one,” according to the plea agreement.

Rahmani speculated that Iwamasa was just doing as he was told. “You have an assistant and if your boss is a drug addict and you want to keep your job, maybe you might do it for that reason.”

Former federal prosecutor, Mark Chutkow, head of government investigations and corporate compliance practice at the law firm, Dykema, views this differently.

The four other defendants allegedly “exploited his addiction,” Chutkow says about Perry.

Iwamasa, however, “was actually injecting this drug into Matthew Perry, so that makes him the most closely tied to what eventually happened.”

Iwamasa faces up to 15 years in prison.

By pleading guilty, he entered into a “cooperating deal” with federal prosecutors, Chutkow says. He is also “the link to all the other defendants,” Chutkow adds, meaning that Iwamasa is potentially a valuable witness.

This may end up leading to a lesser sentence for Iwamasa, Chutkow says.

Iwamasa’s attorneys could not be reached for comment.

If you or someone you know is struggling with substance abuse, please contact the SAMHSA helpline at 1-800-662-HELP.