The police have refused to rule out a criminal homicide charge, according to the Daily Star.

They are said to be looking for doctors or "handlers" who treated the star as friends fear he may have been over prescribed drugs.

"A crack team has been assigned with learning minute by minute what Prince was doing during his final days. But the investigation will also look into his activities over the last two years," a police source said.

It comes as detectives learned the singer had been up for six days before his death.

Prince, 57, was found dead at his home at Paisley Park in Chanhassen, Minnesota, on Thursday. Detectives are understood to have discovered a number of prescription drugs there.

Authorities have said his death is not attributable to suicide or obvious trauma.

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