Michael K. Williams' overdose death was caused by drug dealers who sold him dope laced with fentanyl ... according to the feds who are announcing arrests in the case.
The U.S. Attorney's Office for the Southern District of NY broke the news Wednesday ... saying they had 4 individuals in custody who've been charged in connection with Williams' death last year in Brooklyn.
According to the feds ... a man named Irvin Cartagena made a hand-to-hand transaction with Williams on Sept. 5, 2021 -- allegedly taking cash from the actor and giving him heroin the authorities claim was laced with fentanyl ... which later caused Williams' fatal OD. Law enforcement nabbed Cartagena in Puerto Rico.
Prosecutors allege the exchange between Williams and Cartagena was captured on surveillance video, and posted screenshots they claim show the drug deal going down.
Cartagena is charged with conspiracy to distribute and possess with intent to distribute fentanyl analogue, fentanyl and heroin. He's also being charged with causing Williams' death in connection with the narcotics conspiracy.
All told, he could get life in prison if convicted on all charges.
U.S. Attorney Damian Williams reacted to the arrests, saying ... "This is a public health crisis. And it has to stop. Deadly opioids like fentanyl and heroin don't care about who you are or what you've accomplished. They just feed addiction and lead to tragedy."