Federal investigators have joined the investigation into last month's death of pop music superstar Prince, the U.S. attorney for Minnesota's office said Wednesday.

A statement from that office said it and the Drug Enforcement Administration (DEA) would assist Carver County sheriff's investigators.

"The DEA and US Attorney's Office are able to augment this local investigation with federal resources and expertise about prescription drug diversion," the statement read. "While this remains an ongoing investigation, we will have no further comment."

Prince, known for dozens of hit songs including "Purple Rain", "Let's Go Crazy", and "1999" was found dead April 21 at his Paisley Park estate outside Minneapolis. He was 57. The official cause of death remains undetermined, with the results of an autopsy and toxicology tests pending.

Earlier Wednesday, a Minnesota attorney said Prince's representatives reached out to a California doctor who specializes in addiction treatment the day before Prince died to set up an urgent meeting with the singer. The attorney, William Mauzy, said the reps told Dr. Howard Kornfeld that Prince was dealing with a "grave medical emergency."

Dr. Kornfeld reportedly couldn’t clear his schedule to see Prince until April 22, so he sent his son Andrew instead. Mauzy said that Andrew Kornfeld was going to try and persuade Prince to go into treatment in California and even took a red-eye flight from San Francisco the night Prince’s people called.

Mauzy told the Star-Tribune that when Andrew Kornfeld arrived at the Paisley Park compound at 9:30 a.m. on April 21, Prince’s representatives couldn’t find him. Andrew Kornfeld was one of three people who were with Prince’s body and called emergency dispatchers they were at Prince’s home.

Investigators are reportedly examining whether Prince died from an overdose of prescription painkillers. According to the Star-Tribune, authorities are looking into how Prince acquired the drugs, as well as any other medications used to treat his addiction.

The Star-Tribune has previously reported that Prince suffered an opioid overdose when his plane made an emergency landing in Moline, Ill., on April 15, less than a week before he died. 

The Associated Press contributed to this report.

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