Jimmy Hoffa's disappearance almost 40 years ago has been the stuff of urban legend, prompting numerous theories about what happened to the former Teamsters leader.
The FBI saw enough merit in a reputed Mafia captain's tip to once again this week break out the digging equipment to search for the remains in an Oakland Township field, about 25 miles north of Detroit.
The feisty Hoffa was last seen about 20 miles away on July 30, 1975, outside a restaurant where he was supposed to meet with a New Jersey Teamsters boss and a Detroit Mafia captain.
Hoffa is presumed dead. His body has never been found — but not for a lack of trying.
Previous tips about Hoffa's remains have led police and the FBI to search unsuccessfully in at least six other sites from Michigan to New Jersey:
— In September 1975, shortly after Hoffa was reported missing, Michigan State police and local authorities used a backhoe to look for him on property in Waterford Township.
— In December 1975, the search moved from Michigan to a rubble field in Jersey City, N.J.
— In July 2003, authorities dug beneath an underground pool at a home in Hampton Township, Mich., for a briefcase an informant said contained a syringe and evidence that Hoffa might have been injected with drugs or poison. No briefcase was found.
— In May 2004, police ripped up floor boards from a Detroit house where one-time Hoffa ally Frank Sheeran claimed to have killed him. The FBI crime lab ultimately concluded that blood found on the floorboards was not Hoffa's.
— In May 2006, the FBI called in agents, archaeologists, anthropologists and cadaver-sniffing dogs to search for Hoffa's body at Hidden Dreams Farm in Milford Township. The two-week search at the mid-Michigan horse farm cost about $250,000. It was one of the most extensive searches for Hoffa, with a demolition crew taking apart a barn.
— In September 2012, authorities drilled for soil samples in the floor of a shed in the Detroit suburb of Roseville after police were told by a source that Hoffa was buried beneath the driveway. Tests showed nothing.
Other theories have emerged over the years, including:
— In 1982, self-described mafia murderer Charles Allen, who served prison time with Hoffa and participated in the federal witness-protection program, told a U.S. Senate committee that Hoffa was killed and his body was "ground up in little pieces, shipped to Florida and thrown into a swamp."
— In 1989, self-described hit man Donald "Tony the Greek" Frankos claimed Hoffa was buried under Giants Stadium in East Rutherford, N.J. The FBI found no evidence to support the claim.
— In 2006: New Jersey mob hit man Richard "The Iceman" Kuklinski, who died earlier that year, claimed in a book that he killed Hoffa and put his body in a car that was sold as scrap metal. Kuklinski's book, "The Ice Man: Confessions of a Mafia Contract Killer," contended he received $40,000 for the slaying.
Still another theory has it that Hoffa was obliterated in a mob-owned fat-rendering plant that later burned down.
Take a look through photos of Hoffa and the search for his remains over the last three decades.