(CNN) -- FBI agents and local police searched farmland Wednesday afternoon outside Detroit, Michigan, after receiving a tip about the disappearance of former Teamsters union leader Jimmy Hoffa.
The search was being conducted in Milford Township, 30 miles west of Detroit. Police from nearby Bloomfield Township were assisting the FBI agents.
Aerial footage from the scene showed at least 15 people outside of a barn, most of whom were digging a rectangular hole.
Hoffa was last seen July 30, 1975. The FBI has a sample of his DNA.
Hoffa was 62 at the time of his disappearance. He had been released early from prison by President Richard Nixon on condition that he not seek high union office.
He had served time for mail fraud at the federal penitentiary in Lewisburg, Pennsylvania.
In May 2004, authorities in Oakland County, Michigan, removed floorboards from a Detroit home to look for traces of blood that might have been linked to his disappearance. Milford Township is in Oakland County.
Authorities went to the Detroit home in 2004 after a biography of former Teamsters official Frank Sheehan stated that Sheehan shot Hoffa in the home, just beyond the front door.
Sheehan, who was considered a confidant of Hoffa's, died in December 2003.