Prince performs during the halftime show at the Super Bowl in 2007.

Photo: AP

An autopsy found he died of an accidental overdose of fentanyl, a synthetic opioid 50 times more powerful than heroin.

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The investigative materials – including documents , photos and videos – were posted online Thursday afternoon. Several images show the music superstar's body on the floor of his Paisley Park estate, near an elevator. He is on his back, his head on the floor, eyes closed. His right hand is on his stomach and left arm on the floor.

The documents include interviews with Prince's inner circle. That included longtime friend and bodyguard Kirk Johnson, who told investigators that he had noticed Prince "looking just a little frail," but said he did not realise he had an opioid addiction until he passed out on a plane a week before he died.

"It started to all making sense though, just his behaviour sometimes and change of mood and I'm like, 'oh this is what, I think this is what's going on.' That's why I took the initiative and said, 'let's go to my doctor because you haven't been to the doctor, let's check it all out,'" Johnson said, according to a transcript of an interview with investigators.

Johnson said after that episode, Prince cancelled some concerts as friends urged him to rest. Johnson also said that Prince "said he wanted to talk to somebody" about his addiction.

Surveillance footage of Prince entering the clinic of Dr. Michael Todd Schulenberg on April 20, 2016, the day before he was found dead of an accidental fentanyl overdose.

Photo: Carver County Sheriff's Office

Johnson asked his own doctor, Michael Todd Schulenberg, to see Prince on April 7, 2016. Schulenberg told authorities he gave Prince an IV; authorities said he also prescribed Vitamin D and a nausea medication – under Johnson's name. Johnson then called Schulenberg on April 14, asking the doctor to prescribe a pain medication for Prince's hip. Schulenberg did so, again under Johnson's name, Metz said.

On the night of April 14 to April 15, Prince passed out on a flight home from Atlanta, and the private plane made an emergency stop in Moline, Illinois. The musician had to be revived with two doses of a drug that reverses effects of an opioid overdose.

A paramedic told a police detective that after the second shot of naloxone, Prince "took a large gasp and woke up," according to the investigative documents. He said Prince told paramedics, "I feel all fuzzy."

A nurse at the hospital where Prince was taken for monitoring told detectives that he refused routine overdose testing that would have included blood and urine tests. When asked what he had taken, he didn't say what it was, but that "someone gave it to him to relax." Other documents say Prince said he took one or two pills.

A fan cries at a makeshift memorial created in remembrance of singer Prince outside Apollo Theatre in New York , Friday, April 22, 2016.

Photo: Andres Kudacki

The documents show that Johnson contacted Schulenberg again on April 18, and expressed concern that Prince was struggling with opioids. At that time, Schulenberg told investigators, Johnson apologised for asking the doctor to prescribe the previous painkiller.

An assistant to Prince told investigators that he had been unusually quiet and sick with the flu in the days before he was found dead. Meron Bekure said she last saw Prince a day earlier, when she was going to take him to the doctor for a checkup but that Prince told her he would go with Johnson instead.

On that day, Schulenberg saw Prince and ran some tests and prescribed other medications to help him. A urinalysis came back positive for opioids. That same day, Paisley Park staffers contacted California addiction specialist Dr. Howard Kornfeld. The doctor sent his son, Andrew, to Minnesota that night, and the younger Kornfeld was among those who found Prince's body. Andrew Kornfeld was carrying buprenorphine, a medication that can be used to help treat opioid addiction.

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Andrew Kornfeld told investigators that Prince was still warm to the touch when he was found, but that rigor mortis had begun to set in.

The documents also show that Prince's closest confidants knew he was a private person and tried to respect that, with Johnson saying: "That's what pisses me off cause it's like man, how did he hide this so well?"

Metz said some of Prince's friends might have enabled him as they tried to protect him.

"There is no doubt that the actions of individuals will be criticised, questioned and judged in the days and weeks to come," Metz said. "But suspicions and innuendo are categorically insufficient to support any criminal charges."

The US attorney's office also said Thursday it had no credible evidence that would lead to federal criminal charges. A law enforcement official close to the investigation said that the federal investigation is now inactive unless new information emerges. The official spoke on condition of anonymity because the federal case remains open.

But federal authorities announced that Schulenberg had agreed to pay $30,000 to settle a civil violation from the allegation that he illegally prescribed the opioid oxycodone for Prince in Johnson's name. Schulenberg admitted to no facts or liability in the settlement, which includes stricter monitoring of his prescribing practices, and authorities said he is not the target of a criminal investigation.

Oxycodone, the generic name for the active ingredient in OxyContin, was not listed as a cause of Prince's death. But it is part of a family of painkillers driving the US's addiction and overdose epidemic, according to the Centres for Disease Control and Prevention. Nearly 2 million Americans abused or were addicted to prescription opioids, including oxycodone, in 2014.

AAP

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