Authorities are shedding light on how Matthew Perry's personal assistant allegedly played a part in his death.

Kenneth Iwamasa admitted to injecting the Friends alum with multiple doses of ketamine—a controlled substance known for its dissociative effects—without any prior medical training on Oct. 29, the day Perry was found dead in a hot tub at his Los Angeles home, according to the Department of Justice.

Iwamasa, 59, pleaded guilty to one count of conspiracy to distribute ketamine causing death in the investigation into Perry's passing, prosecutors said in an Aug. 15 press release.

He is one of the five people who have been charged in connection to Perry's death, which a medical examiner previously determined to have been caused by "the acute effects of ketamine" in drug and drowning-related accident.

Jasveen Sangha—a 41-year-old who authorities call “The Ketamine Queen"—is facing one count of conspiracy to distribute ketamine, one count of maintaining a drug-involved premises, one count of possession with intent to distribute methamphetamine, one count of possession with intent to distribute ketamine and five counts of distribution of ketamine, per the DoJ.

Meanwhile, Dr. Salvador Plasencia, 42, has been charged with one count of conspiracy to distribute ketamine, seven counts of distribution of ketamine and two counts of altering and falsifying documents or records related to the federal investigation.

Others charged in connection to Perry's death include 54-year-old Erik Fleming—who the DoJ said pleaded guilty to two ketamine-related charges after admitting to authorities that he distributed the ketamine that killed the actor—and Dr. Mark Chavez, a San Diego-based physician who prosecutors said admitted in a plea agreement to selling ketamine to Plasencia.

Chavez, 54, has agreed to plead guilty to one count of conspiracy to distribute ketamine, according to the DoJ.

"We allege each of the defendants played a key role in his death by falsely prescribing, selling, or injecting the ketamine that caused Matthew Perry’s tragic death," Anne Milgram of the U.S. Drug Enforcement Administration said in a statement. “Matthew Perry’s journey began with unscrupulous doctors who abused their position of trust because they saw him as a payday, to street dealers who gave him ketamine in unmarked vials."

Authorities accused Plasencia working with Chavez—who previously operated a ketamine clinic—in late September 2023 to obtain the drug to sell to Perry, writing in an alleged text message, "I wonder how much this moron will pay."

Plasencia then supplied ketamine to Perry—who had been receiving ketamine infusion therapy to treat depression and anxiety—and Iwamasa "outside the usual course of professional practice and without a legitimate medical purpose," the DoJ alleged in their Aug. 15 press release. 

Prosecutors also accused Fleming and Sangha of supplying Iwamasa with additional ketamine in October 2023, which the assistant allegedly used to inject Perry—whose had been public about his addiction struggles—through instructions and syringes he received from Plasencia.

In Perry's autopsy report, previously obtained by E! News, the medical examiner said the 54-year-old was "reportedly clean for 19 months" prior to his death.

In an Aug. 15 statement, U.S. attorney for the Central District of California Martin Estrada said that those charged in the Whole Nine Yards star's case "cared more about profiting off of Mr. Perry than caring for his well-being."

"Drug dealers selling dangerous substances are gambling with other people’s lives over greed," he continued. "This case, along with our many other prosecutions of drug-dealers who cause death, send a clear message that we will hold drug-dealers accountable for the deaths they cause.”

E! News has reached out to attorneys for Iwamasa, Sangha, Plasencia, Chavez and Flemming but has not heard back.