A Hawaii crime boss who died in federal detention this month was killed by an opioid overdose, Honolulu’s medical examiner said Tuesday. Michael Miske, 50, died of “toxicity of fentanyl and para-fluorofentanyl,

Michael Miske died of "toxicity of fentanyl and para-fluorofentanyl," the medical examiner’s office said in a statement obtained by AP. The death appears to have been accidental.

Michael Miske Jr., who was convicted in July of operating one of the most notorious organized crime rings in Hawaiʻi, died of a fentanyl overdose in the Federal Detention Center, according to city officials. Miske, 50, was found dead in his cell Dec. 1.