Michael K. Williams may have died of a fentanyl overdose inside his Brooklyn penthouse on Monday, leading police to launch an investigation in an effort to find the actor’s drug dealer, according to NYPD sources.

The American actor and Wire star was 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 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.

In the video, Morgan said:

‘I had a misfortunate accident. Don’t cry for me. Cry for all the others, man.’

This comes just less than seven months after Williams revealed that he started therapy for the first time after being deeply affected by his role in Body Brokers,  his final film.

‘I just started therapy, you know, and really taking that seriously and starting to unpack, like you said, the critic in my head and what and how that has affected my –  my actions, my responses to certain situations, my relationships,’ Williams said during the February 25 Tamron Hall Show.