New information from the investigation into Prince’s death shows he may have unwittingly ingested the incredibly powerful synthetic drug that killed him, fentanyl.

Prince weighed 112 pounds when he died, from a dose of the opioid fentanyl that was so powerful it would have “killed anyone, regardless of their size,” the Minneapolis Star Tribune reported Sunday (Aug. 21). Investigators found counterfeit drugs in his home that looked like a Watson Laboratories blend of acetaminophen and hydrocodone, but the pills actually contained fentanyl, the AP reported, citing a source close to the investigation.

Investigators are “leaning toward the theory he took the pills not knowing they contained the drug,” the Minneapolis paper reported. He likely took the drug for the first time in the 24 hours before he died, as earlier tests did not show fentanyl in his system, the AP reported.

Fentanyl is legally prescribed for pain, particularly in cancer patients, and often administered by a patch, but the drug was declared a “threat to health and public safety” by the US Drug Enforcement Administration last year. It has similar euphoric effects to heroin and morphine, but is many times more fatal in lower doses, and illegal labs are lacing it with heroin, the agency said.

“It seems more and more likely that Prince became a casualty of what is being called a new national crisis of deadly counterfeit pills,” the Star Tribune wrote. Synthetic drugs like fentanyl and flakka from Chinese labs have flooded the US in recent years, in part because drug companies in China openly offer the raw materials to make them and drug import and export laws are easy to circumvent.

Illegal Chinese labs have been tweaking chemical compositions of fentanyl and other synthetic drugs to get around China’s export laws and the US’s import rules, by altering the molecular composition slightly. Hundreds of thousands of counterfeit pills containing potentially lethal doses of fentanyl and other synthetic drugs have entered the US, from labs in China that are “mass-producing” the pills, the DEA said last month.