An excavating machine on Wednesday began ripping chunks out of a barn on a horse farm where FBI agents and police have searched since last week for the body of former Teamsters union boss Jimmy Hoffa, who vanished in 1975 after serving a prison term for looting the pension fund.

No trace of Hoffa has ever been found, and no one has ever been charged in his disappearance.

Hoffa was last seen on the night he was scheduled to have dinner at a restaurant about 20 miles from the farm. He was supposed to meet with a New Jersey Teamsters boss and a Detroit Mafia captain, both now dead.

Over the years, Hoffa's disappearance spawned endless theories — that he was entombed in concrete at Giants Stadium in the New Jersey Meadowlands; that he was ground up and thrown to the fishes in a Florida swamp; that he was obliterated in a mob-owned fat-rendering plant that has since burned down.

Agents plan to spend a couple weeks trying to determine if Hoffa is buried somewhere on the farm about 30 miles northwest of Detroit. Officials have said the search would involve cadaver dogs, demolition experts, archaeologists and anthropologists.

A government investigator said last week that Donovan Wells, who lived on the land at the time, was the one who gave the FBI the tip that has sparked the intense effort to solve a legendary mystery.

Wells' lawyer, Joseph J. Fabrizio, said that his client told the FBI about the location in 1976.

The investigator said that Wells was not that forthcoming 30 years ago, and that he recently passed a polygraph exam. The investigator is familiar with the current dig and spoke on condition of anonymity because some of his information comes from records that have been ordered sealed by a federal judge.