At a press conference last night, Carver County sheriff Jim Olson said there were “no obvious signs of trauma” on Prince’s body.
“We have no reason to believe this was a suicide,” he said.
The American musician was pronounced dead at his Paisley Park estate near Minneapolis on Thursday.
Mr Olson said Prince was last time seen alive at 8pm on Wednesday at Paisley Park. He said friends and associates had been trying to reach Prince on Thursday morning, but were unsuccessful.
An autopsy was performed yesterday on the body of the 57-year-old. Information about his “medical and social history” was gathered, said the Midwest Medical Examiner’s Office. The postmortem examination was completed after four hours and Prince’s body was to be released to his family.
A spokeswoman for the Midwest Medical Examiner’s Office said it would not release information from the postmortem until “all results are obtained” and the findings of a toxicology scan “could likely take weeks”.
Celebrity news website TMZ reported that Prince had overdosed on a pain-killer called Percocet when his private jet made an emergency landing in on April 15 in Atlanta, Georgia.
The Purple Rain star was taking the drug for a hip problem after having corrective surgery around six years ago, TMZ said.
A day after Prince was rushed to hospital on April 15, he hosted a dance party at Paisley Park where fans said he “seemed happy” and appeared to look healthy.
Gretchen Richardson, 27, told the Press Association: “It was just a short appearance. He just said: ‘Save your prayers for a couple of days. I’m OK. I’m here, thank you. I appreciate it.’ ”
Jeremiah Freed, who also attended the event, said that Prince told the crowd: “Just wait a few days before saying your prayers.”
Tributes have flooded in for the singer, whose full name was Prince Rogers Nelson. US president Barack Obama described Prince as a “creative icon”.
Madonna said he was a “true visionary”, while Elton John shared a picture of Prince on his Instagram page, writing: “The greatest performer I have ever seen.”
Sales of Prince’s music soared after news broke of the pop star’s death, and fans continued to leave floral tributes at Paisley Park many hours after his death was announced.
Thousands of Prince fans also gathered at the club in Minneapolis where he filmed Purple Rain as the venue hosted a free all-night dance party in his honour. Two more events are planned at the venue over the weekend.
Mr Obama revealed he played Prince’s music at the US ambassador’s home before meeting British prime minister David Cameron in London. Speaking at a press conference at the Foreign Office, he said: “I love Prince because he put out great music and he was a great performer.
“I didn’t know him well. He came to perform at the White House last year and was extraordinary and creative and original and full of energy. It’s a remarkable loss. I’m staying at Winfield House, the US ambassador’s residence. It so happens our ambassador has a turntable so this morning we played ‘Purple Rain’ and ‘Delirious’ before we left the house for important bilateral meetings like this.”