An investigation has revealed that mislabeled pills found at Prince’s Paisley Park estate contain fentanyl, according to the Associated Press — two months after an autopsy revealed that the legendary musician died from an overdose of the drug.

The AP, citing an official who spoke on the condition of anonymity, said at least one of the pills of the more nearly two dozen found tested positive for fentanyl, a highly addictive opioid 50 times more powerful than heroin. The counterfeit pills were mislabeled “Watson 385,” a stamp that’s supposed to indicate pills containing a mix of acetaminophen and hydrocodone.

It’s currently not clear how Prince obtained the drugs. The official told the AP that Prince did not have a prescription for any controlled substances in the 12 months before his death. The investigation is ongoing.

Some of the other drugs police found also reportedly contained codeine, and some were not controlled substances. An aspirin bottle found on his estate contained more than 60 pills, the AP reports. Authorities also apparently found ten oxycodone pills in a bottle with someone else’s name on it (police are not revealing the name).

Prince was found dead in his home outside of Minneapolis, Minn., on April 21 at the age of 57. His autopsy results were released in June.