The American actor and Wire star were found dead on Monday afternoon, September 6, by a concerned relative inside his apartment in a Williamsburg high-rise. Police who went to the scene were said to have recovered drug paraphernalia.

It was previously reported that heroin may have claimed the life of the 54-year-old Boardwalk Empire alum, but two senior NYPD officials told NBC New York that fentanyl was being eyed as the culprit.

Fentanyl is a powerful synthetic opioid that is similar to morphine but is 50 to 100 times more potent. It can cause death when taken in high doses or when combined with other substances.

The medical examiner’s office will conduct an autopsy to determine Williams’ cause and manner of death.

TMZ reported, citing unnamed law enforcement sources, that police were trying to find the person or people who supplied Williams with the drugs.

Williams’ death came just six days after he posted a message imploring his fans to not cry for him. The 54-year-old posted on Instagram a video of Tracy Morgan telling fans ‘Don’t cry for me. OK’, after the comedian’s near-fatal 2014 limousine crash.

Show director, co-writer, and producer Ava DuVernay took to Twitter to thank the real-life series subjects Antron McCray, Kevin Richardson, Yusef Salaam, Raymond Santana, and Korey Wise who have since been dubbed The Exonerated Five.

DuVernay also picked up writing and directing noms for the series, while Jharrel Jerome, Aunjanue Ellis, Niecy Nash, Asante Black, John Leguizamo, and Michael K. Williams were among the series stars recognized for their acting performance.

When They See Us is one of the most popular series on the streaming platform, showing up on more than 23 million accounts worldwide.