(CNN) -- The FBI is planning to dig in a Detroit-area field Monday in a hunt for the remains of former Teamsters boss Jimmy Hoffa, according to a law enforcement source with direct knowledge of the investigation.

Agents on Monday morning were executing a search warrant for a field in Oakland Township, north of Detroit, based in part on information provided by Tony Zerilli, a man alleged to have been a mobster.

Earlier this year, Zerilli told New York's NBC 4 that Hoffa was buried in a Michigan field about 20 miles north of where he was last seen in 1975.

The FBI has spent months looking into Zerilli's claims before seeking court authorization to excavate the field and look for evidence of a shallow grave, according to the source.

Hoffa, then 62, was last seen on July 30, 1975, outside a Detroit-area restaurant. The FBI said at the time that the disappearance could have been linked to Hoffa's efforts to regain power in the Teamsters and to the mob's influence over the union's pension funds.

Hoffa's disappearance and presumed death has vexed investigators for almost four decades. As recently as October, soil samples were taken from a home in the suburban Detroit community after a tipster claimed he saw a body buried in the yard a day after Hoffa disappeared in 1975.

The soil samples were tested, and showed no evidence of human remains or decomposition.

Zerilli, freed in 2008 after his last prison sentence, was convicted of crimes in connection with organized crime in Detroit. Keith Corbett, a former U.S. attorney, told CNN earlier this year that Zerilli headed a Detroit organized crime family from 1970 to 1975, but was in prison when Hoffa disappeared.

Zerilli told CNN affiliate WDIV-TV that a "Mafia enforcer" informed him that Hoffa was buried in the Oakland Township field as a temporary measure, and that the remains were to be moved to another spot near a hunting lodge after the heat died down from a massive police attempt to find Hoffa.

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