Investigators want to interview a California doctor and his son about a prescription drug the son brought for Prince before the singer was found collapsed in an elevator at his Minnesota home.
The official told The Associated Press investigators also want to know if Dr Howard Kornfeld and son Andrew Kornfeld had a longer-term medical relationship with Prince. Neither is accused of wrongdoing.
The law enforcement official had been briefed on the investigation and spoke on condition of anonymity because he wasn't authorised to speak to the media.
The Kornfelds' lawyer, William Mauzy, said Prince's staff called Howard Kornfeld on April 20. He sent his son on an overnight flight with the drug buprenorphine. Andrew Kornfeld found Prince unresponsive and did not administer the drug.
