In the book "I Heard You Paint Houses", Frank Sheerhan basically confesses to killing Hoffa and he speculates that Hoffa was cremated. The mob wanted Hoffa dead. They had a connection with a funeral home in Detroit. If you haven't read the book, it is full of interesting information; not only about Hoffa, but JFK and mob hits around NYC and Philly.
Whoever exalts himself will be humbled, whoever humbles himself will be exalted - Matthew 23:12