Authorities have "no reason to believe" Prince took his own life and there were "no obvious signs of trauma" on the his body, US police said.
The music superstar died aged 57 at his Paisley Park estate near Minneapolis on Thursday after he was found collapsed in a lift.
Speaking at a press conference at Carver County Courthouse in Chaska, Minnesota, Sheriff Jim Olson refused to comment on reports that Prince had been taking a powerful painkiller before his death.
He said it was "still under investigation" whether foul play was involved.
Prince was last seen at 8pm the night before his death when he was dropped off at Paisley Park, Olson said.
Staff members had been unable to reach him and he had been alone at the estate. He was found collapsed in a lift by staff members.
"There were no obvious signs of trauma on the body at all," Olson said.
"We have no reason to believe at this point that this was a suicide."
Asked whether there was any reason to believe foul play was involved, Olson said: "We have no reason to believe at this time it was a suicide, the rest of it is under investigation."
A post-mortem examination took place on Friday, where information about Prince's "medical and social history" was gathered, the Midwest Medical Examiner's office said.
Prince's body has been released to his family but a cause of death may not be made public for weeks, officials said.
Celebrity news website TMZ reported that Prince had overdosed on a painkiller called Percocet when his private jet made an emergency landing in Atlanta, Georgia, on April 15, six days before his death.
The star was taking the drug for a hip problem after having corrective surgery around six years ago, TMZ said.
A spokeswoman for the medical examiner's office said it would not release information from the post-mortem examination until "all results are obtained" and the findings of a toxicology scan "could likely take weeks".