Hoffa probably killed/dumped in incinerator by Provenzano's mob associate..

https://www.thedailybeast.com/martin-scorseses-the-irishman-is-a-big-lie-heres-what-really-happened-to-jimmy-hoffa

Hoffa was taken to a secluded location nearby, knocked unconscious, then put in the trunk of the Giacalone car and taken to Central Sanitation, a Mafia-operated waste disposal facility in an industrial area. Investigators speculated loud machinery was activated, Hoffa was shot in the head, then his body was dumped in a high-intensity industrial incinerator. In this scenario he became part of the ozone layer shortly after he disappeared. No body, no evidence. Central Sanitation burned to the ground about the time FBI agents began snooping around as part of the Hoffa investigation.

Dan Moldea, the author, is among those of us who believe the late Sal Briguglio, Provenzano’s close associate, is the guy who whacked Hoffa with the help of his brother Gabe and Thomas Andretta. Briguglio was murdered gangland-style in New York in March, 1978. He was about to go on trial with Provenzano for the Castellito murder.