HONOLULU (AP) -- Honolulu's medical examiner says a Hawaii crime boss who died in federal detention this month was killed by an opioid overdose. Michael Miske died of "toxicity of fentanyl and para-fluorofentanyl." The medical examiner says the 50-year-old's death appears to have been accidental, but the case is still under investigation. An autopsy report will likely take at least another 30 days. It's not clear how Miske got ahold of fentanyl or para-fluorofentanyl while at the Honolulu Federal Detention Center. Para-fluorofentanyl is a synthetic opioid that appears in illicit drugs and is more potent than fentanyl. The Bureau of Prisons did not immediately respond to an email seeking comment Tuesday.