MILFORD TOWNSHIP, Mich. -- Investigators have started digging at Hidden Dreams Farm in Milford Township, Mich., in a search for the human remains of Jimmie Hoffa, according to the search warrant obtained by The Associated Press.

The FBI said Thursday it may take a while to find what it's looking for.

Special Agent Daniel Roberts said the search for clues in the 1975 disappearance of Hoffa, once a well known labor leader, is expected to take at least a couple of weeks.

Agents will probably have to remove a barn in order to complete the search.

Roberts said the information that led agents to the farm is the "best lead" he's come across in the Hoffa case in the two years that he's headed the FBI's operation in Detroit.

Authorities with cadaver dogs and heavy construction equipment are searching the property. The FBI has also brought in anthropologists and archaeologists from Michigan State University for assistance.

Federal agents will not release the name of the person or persons who gave them the tip, but they did say that the tip included information on a group of people who used to meet on the same piece of land 30 years ago, according to federal officials.

A law enforcement source in Washington said the property had been the scene of suspicious activity the day Hoffa disappeared. The source also said organized crime figures used the area for meetings, but stopped after Hoffa vanished.

The FBI has made contact with Hoffa's daughter who resides in St. Louis, but no other information has been released.