Several key people had contact with Prince before his death, and were involved in the investigation that followed.
Despite an extensive, thorough investigation into the musician's death, Metz has concluded: "Investigators were unable to determine how the singer obtained the counterfeit pills".
Prince took a lookalike, counterfeit version of the drug that was far more powerful and unsafe, Mr Metz noted.
The investigative materials - including documents, photos and videos - were posted online on Friday.
Images just released show Paisley Park as a colorful, eclectic space that was the beloved home of Prince, where the superstar had relaxed, recorded music and threw parties. His head us on the floor, eyes closed, right hand on his stomach, and left arm on the floor.
The documents include interviews with Prince's inner circle. Judith Hill, one of Prince's protégées who was on the Moline flight, said to investigators that he had been exhausted on the way to Atlanta, even telling her, "Oh man, I love sleeping more, maybe it means I've done all I'm supposed to do on this earth".
Johnson said after that episode, Prince cancelled some concerts as friends urged him to rest.
Surveillance footage showed the bodyguard Johnson at a Walgreens, picking up a prescription hours before Prince's death. Authorities say Schulenberg did so, under Johnson's name.
At the hospital, Prince refused medical tests. When Prince took a large gasp of air and woke up, he looked at Johnson without saying anything and Johnson told paramedics, "Prince feels fine", according to documents.
Metz says nothing in the evidence suggests Prince knowingly took it or that there was a "sinister motive".
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Prince is shown on his back next to a sun design on the carpet. He was among those who found Prince dead.
"Prince had no idea he was taking a counterfeit pill that could kill him", Metz said. Schulenberg also ran unspecified tests on Prince and showed up at Paisley Park on the day Prince died. After that, Johnson said he and others reached out to an addiction specialist.
The doctor sent his son, Andrew, to Minnesota that night, and the younger Kornfeld was among those who found Prince's body. Prince's doctor had prescribed a medication used to treat opioid withdrawal.
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.
A couple of associates said they had noticed changes in Prince's demeanor and behavior.
"There is no doubt that the actions of individuals will be criticised, questioned and judged in the days and weeks to come", Metz said.
The source of those pills is unknown and no one has been charged in Prince's death. A federal investigation is now inactive unless new information comes forward.
The official spoke on condition of anonymity because the federal case remains open. Court documents also allege that on April 14, Schulenberg wrote out a prescription for oxycodone and put it in Johnson's name, intending the drug to go to Prince.
The singer passed away in April 2016 after being found unresponsive in his Paisley Park mansion.
The underground market for counterfeit prescription pain pills is brisk and can be highly anonymous, said Carol Falkowski, CEO of Drug Abuse Dialogues, a Minnesota-based drug abuse training and consulting organisation.