(AP Photo/Chris O'Meara, File).
FILE - In this February 4, 2007, file photo, Prince performs during the halftime show at the Super Bowl XLI football game in Miami. But the documents don't reveal the big missing piece in the criminal investigation: Where did Prince get the fentanyl that killed him?
(Carlos Gonzalez/Star Tribune via AP, File). Almost a year after Prince died from an accidental d.
Several search warrants were unsealed Monday near the one-year anniversary of Prince's death of a fentanyl overdose.
Search warrants and other documents related to criminal cases are normally public record, but authorities had requested all documents related to the Prince death investigation be sealed as the probe proceeded. And news that he died of an overdose of fentanyl - a synthetic drug 50 times more powerful than heroin - surprised and saddened those who knew him as someone with a reputation for clean living.
Detectives were "made aware by witnesses that were interviewed, that Prince recently had a history of going through withdrawals, which are believed to be the result of the abuse of prescription medication", the documents said.
The incident occurred just days before his death.
Advocates of the drug say the opiate can help addicted patients by offering pain relief with reduced possibility of overdose and addiction.
He went to Paisley Park on April 21 - the day Prince was found - to drop off test results, he said.
About a week before his death, Prince's private jet made an emergency landing early April 15 in Moline, Illinois, on the way back from a performance in Atlanta. Emergency responders administer a shot of Narcan, an opioid antidote, and take him to the hospital.
A search of Prince's home yielded numerous pills in various containers.
Investigators said interviews with those present at Paisley Park when Prince was found - including Meron Bekure, Prince's assistant, and Johnson - gave contradictory statements about what had happened.
Some of the bottles were labeled Aleve and Bayer - common over-the-counter medications - but contained pills marked "Watson 853", the opioid painkiller acetaminophen-hydrocodone.
Authorities said Prince's laptop was not taken during an initial warrant but it became clear later in the investigation that items on it would be significant when they discovered he did not communicate by cellphone, but instead used email and the hard phone line at Paisley Park extensively. The day before Prince died, Paisley Park staffers contacted the California addiction specialist as they were trying to get Prince help.
Some pill bottles had Prince's long-time friend and estate manager Kirk Johnson's name on them.
Messages left with attorneys for Schulenberg and Johnson weren't immediately returned Monday. Schulenberg has an active medical license and is now practicing family medicine in Minnesota.
It's been almost a year since Prince died from an accidental drug overdose at his suburban Minneapolis estate, yet investigators still haven't interviewed a key associate or asked a grand jury to consider whether criminal charges are warranted, according to an official with knowledge of the investigation.
Search warrants executed by local authorities, likely including one from the first search of Paisley Park, are due to be unsealed Monday.
A prescription monitoring warrant, issued as part of the investigation, reveals the singer was never prescribed any of the controlled substances that were found at Paisley Park.
Lyrics for the song, "U Got the Look", were also found in that suitcase, written in Prince's handwriting. Kornfeld can not clear his schedule to fly to Minnesota immediately, so he sends his son, Andrew, on an overnight flight.
Andrew Kornfeld was carrying buprenorphine, a medication that can be used to help treat opioid addiction.
Investigators have said little about the case over the previous year, other than it is active. The official who spoke to the AP said the case has taken investigators to IL and California, as authorities have interviewed friends, family and any potential witnesses, including the flight crew and hospital staff that were present when Prince overdosed on the plane.
AP Medical Writer Carla K. Johnson contributed to this story from Chicago.