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Jimmy Hoffa (search) became the leader of the Teamsters Union (search) in 1957 but was sent to prison 10 years later for jury tampering and fraud. He was pardoned in 1971 after giving up the union presidency and in 1975 attempted a comeback — one that never was able to happen because he disappeared. Below is a timeline of the Hoffa case:

1975

July 30: Jimmy Hoffa, 62, disappears. Hoffa was supposed to have met at the Machus Red Fox restaurant in Detroit with Frank Sheeran, a local Teamsters official from Detroit, and mobsters Anthony “Tony Jack” Giacalone and Anthony “Tony Pro” Provenzano. Hoffa is last seen in the parking lot.

July 31: Hoffa’s car, a green Pontiac Grand Ville, is found unlocked in the restaurant parking lot.

August 2: The FBI takes over the investigation. More than 200 FBI agents are assigned to the case in New Jersey, Detroit and at least four other cities. Over the next decade, the FBI compiles more than 70 volumes of files covering some 16,000 pages.

August 8: The FBI searches Hoffa’s car, finding fingerprints of family friend Charles “Chuckie” O’Brien on a soda bottle.

August 21: Police dogs, working off clothes Hoffa wore the day before his disappearance, indicate Hoffa’s scent was in the rear of a car O’Brien borrowed from his friend Joe Giacalone, son of Anthony Giacalone.

September 2: A grand jury in Detroit begins to investigate the Hoffa disappearance. Over the next six months, at least 50 people with ties to the mob are called to testify. One of those who testifies is Sheeran, who takes the Fifth.

1982

Mobster Charles Allen, who served time in prison with Hoffa, tells a U.S. Senate committee that Hoffa was killed on Provenzano’s orders. He claimed that his body was “ground up in little pieces, shipped to Florida and thrown into a swamp.”

1983

Authorities declare Hoffa officially dead, although the body was never found.

1989

Kenneth Walton, the head of the FBI's Detroit office, tells The Detroit News he knows what happened to Hoffa. “I’m comfortable I know who did it, but it’s never going to be prosecuted because… we would have to divulge informants, confidential sources,” he said. Hoffa’s daughter, Barbara Crancer, files a Freedom of Information Act lawsuit against the FBI, demanding the bureau’s reports on Hoffa’s disappearance.

Donald “Tony the Greek” Frankos claims Hoffa is buried under Giants Stadium in East Rutherford, N.J. The FBI finds no evidence to support the claim.

1993

The U.S. Court of Appeals reverses a ruling ordering Crancer to get the FBI files on her father’s disappearance.

1999

Author Charles Brandt begins interviewing Frank Sheeran, a process that lasted nearly five years, on audio tape to document Sheeran's admission that he's the one who fired the weapon that killed Hoffa.

Sheeran's story is that on the day Hoffa disappeared, Chuckie O'Brien drove Hoffa, Sheeran and mobster Sal "Sally Bugs" Briguglio to a house in Detroit. Hoffa and Sheeran went into the house and the other two men drove off.

Sheeran says he shot Hoffa twice behind the right ear as part of a mob hit to keep Hoffa from reclaiming power in the Teamsters. After the murder, Sheeran says he left the house and was told Hoffa was cremated.

2001

Current and former FBI agents and federal prosecutors meet in March after DNA tests find a match between a hair found in the back of the car driven by O’Brien and a hair in Hoffa’s hairbrush. In June, police comb Hoffa's car for clues.

In May, Sheeran repeats what he told Brandt —  that he killed Hoffa — to Fox News' Eric Shawn. Sheeran also, for the first time, gives directions to the house where he claims the murder took place.

2002

In February, Brandt and Sheeran drive to Detroit where Sheeran points out the house where Hoffa is said to have been killed.

The next month, the FBI says it will refer the Hoffa case to the Oakland County Prosecutor’s Office for possible state charges after agents determine the federal case was stymied because of the length of time since Hoffa disappeared. But five months later, county prosecutors say new DNA evidence is insufficient to bring criminal charges.

2003

July 16: Oakland County authorities dig for a briefcase they say may be buried beneath an underground pool at a home in Michigan’s Thumb area. Authorities say a convicted murderer who helped police find the body of another long-vanished man earlier in the year claims Hoffa is buried in the yard.

Dec. 14: Frank Sheeran dies in a nursing home near Philadelphia. Before his death, Brandt videotapes Sheeran in his hospital bed and on tape Sheeran stands behind his admissions in Brandt's book "I Heard You Paint Houses."

2004

May 28: After a Fox News investigation, which involved a team of crime scene experts discovering indications of blood in the house Sheeran mentioned, Oakland County prosecutors search the home and remove floorboards and other items.

Erinn Morrison compiled this timeline for Foxnews.com