While there are many theories and ideas about who killed Jimmy Hoffa, the generally accepted sequence of events was that:
On the morning of 30 July 1975, Hoffa got a phone call and a few hours later, he left his Orion Lake home to drive to Manchu's Red Fox restaurant in a shopping center at fourteen Mile Road and Telegraph in Detroit. He never returned and his car was found in the shopping center's parking lot, unlocked and abandoned.
In the days, weeks, and months which followed, the FBI fed bits and pieces of a story to eager journalists and the public. The FBI story as embellished by the press came to be accepted as truth. The story involved Hoffa going to the Red Fox restaurant supposedly to meet with two other men, neither of which showed up.
Hoffa waited outside near his car for some time waiting for someone. A maroon Lincoln or Mercury drove up with three men inside. After a brief conversation, Hoffa got into the back seat of the Maroon car and it drove away. Once inside, Hoffa was knocked unconcious and either shot or strangled on the way into Detroit. His body was then disposed of in an incinerator.
Some (especially those close to Hoffa) say that the above is all a government cover-up to what really happened. Because Hoffa did not do the sort of specific things (the details) mentioned in the story.
One of Hoffa's men, Joe Franco, co-authored a book about Jimmy Hoffa titled "Hoffa's Man". In it, he claims to have actually seen something different happen in the parking lot that day. He states that three men in a black Ford LTD pulled in front of Hoffa, just as he was about to drive away. A black man was driving, while two white men in sport coats and ties got out and flashed some sort of badges or identification at Hoffa. They all got into the black car and drove away. Franco tailed them north for a ways, when they turned onto a road leading to Pontiac. Franco continued north to Flint and never saw Hoffa again.
Franco believes that the phone calls earlier were a set up by the government to get him to the parking lot, and that he kidnapping was done by US marshalls or FBI agents.