A medical examiner revealed a Hawaii crime boss died of an opioid overdose while in federal detention.
Michael Miske, 50, was found unresponsive at the facility on December 1.
It was later revealed that he died from "toxicity of fentanyl and para-fluorofentanyl," the medical examiner's office said in a statement shared with ABC News.
"Michael Miske's death was unexpected and may terminate some of the ongoing criminal proceedings," Attorney Clare E. Connors of the United States Attorney's Office in Hawaii said. "The United States spent years investigating Miske's large-scale criminal enterprise and then years preparing for one of the most grueling trials in this office's history. Justice was served in the process but aspects of the case remain unfinished."
Connors said the office is committed to "pursuing recovery of the forfeitable assets" and "will file pleadings in court."
According to ABC News, Miske's death is deemed an accident but the case is still under investigation.
An autopsy report will be revealed to the public in another 30 days, said authorities.
It's not clear how Miske managed to get fentanyl or para-fluorofentanyl while at the Honolulu Federal Detention Center.
He was convicted in July on 13 charges including racketeering conspiracy, murder in the aid of racketeering, and kidnapping resulting in death.
He was accused of orchestrating crimes like the kidnapping of an accountant who owed a debt; the release of a toxic chemical into a rival's nightclubs, and the murder of his late son's best friend.
Miske did not have a criminal history of trafficking or using opioid.
Miske forfeited nearly $28 million in including boats, real estate and artwork following his conviction.
He sentencing was scheduled for January 30.
