06/17/2013 04:44 pm ET Updated Jun 18, 2013

Hoffa Remains May Be Under Field, Feds Dig For Clues In Case Of Jimmy Hoffa Disappearance (PHOTOS)

An alleged mobster's representative said he believes "100 percent" that the final resting place of missing Teamsters boss Jimmy Hoffa has been discovered.

FBI investigators, along with members of the Oakland County Sheriff's Department, swarmed a vacant field in Oakland Township in suburban Detroit on Monday in search of Hoffa's remains. They were led there by a tip from Tony Zerilli, the 85-year-old son of Joseph Zerilli, widely believed in Detroit to have controlled one of the city's most legendary Mafia organizations.

Though Zerilli was in prison at the time of Hoffa's disappearance in 1975, he believes that Hoffa's body was buried at the vacant field in Oakland Township. Land near the plot investigators are searching was once owned by another reputed Mob heavyweight, Jack Tocco. Zerilli said the body is buried beneath two cement slabs in the vacant field, where a barn once stood. Agents used an excavator to clear away debris before attacking the area with shovels on Monday.

According to the Associated Press, Robert Foley, special agent for the Detroit FBI division, told reporters that the agency executed a sealed search warrant on the property but didn't take questions.

Investigators at the site could be seen carrying binders that said "Big Dig 2." A previous search attempt for Hoffa at a farm in Milford, Mich., also located in North Oakland County, was referred to as the "Big Dig."

"It's not like 50-50, maybe," said David Chasnick, attorney for Tony Zerilli, during a press conference. "They think they're going to find it."

If the feds locate Hoffa's remains, it will mark the end of a 38-year-old mystery that has become one of America's most enduring urban legends.

Hoffa, a labor union leader and former president of the Teamster's Union, rose to national prominence before being convicted of fraud and attempted bribery of a juror.

After President Richard Nixon commuted his sentence in 1972, he barred Hoffa from re-establishing himself as the head of the Teamsters. By the time of his disappearance in 1975, Hoffa had lost much of his national influence, but had decided to rekindle his political career.

Hoffa was last seen in the parking lot of the Machus Red Fox, a Bloomfield Township restaurant, around 2:45 p.m. on July 30, 1975. The union boss was never heard from, or seen, again. He was declared dead in 1982, but the search for his remains has continued to this day.

Those who were implicated at the time of Hoffa's disappearance are now dead themselves. Anthony Giacolone, another rumored Mobster who faced speculation that he had arranged the restaurant meeting, died in 2001.

"Many people believe that Mr. Giacalone held a key and carried it to his grave," wrote The New York Times in Giacolone's obituary. New Jersey labor leader Anthony "Tony Pro" Provenzano, who was reportedly a capo in the Genovese crime family, was also rumored to have been at the meeting. He died in 1988.

On a website he's created to promote his new book, tipster Tony Zerilli says he is one of two people alive who could possibly know the whereabouts of Hoffa's remains. "Mr. Zerilli is one of them, and he is the only one talking," he writes.

Even if Hoffa's remains are found, another question remains unanswered: who else knows what really happened during the final, unknown hours of Jimmy Hoffa's life?

Below, see scenes from Monday's search and the futiles ones of the past.

The Search For Jimmy Hoffa, Present And Past