The FBI is using everything it has to find the remains of Jimmy Hoffa after agents received what they say is "a fairly credible lead" on the former Teamsters boss' 1975 disappearance.
The arsenal includes forensic experts from the bureau's Washington laboratory and a team of scientists that includes anthropologists, archaeologists, engineers and architects who will accompany local police and cadaver dogs for the next two weeks.
The architects and engineers are needed because authorities may need to remove a 30-foot-by-100-foot horse barn during their search, said Daniel D. Roberts, special agent in charge of the FBI's field office in Detroit, Michigan.
Authorities converged Wednesday on an 80-acre horse farm after receiving and confirming a tip that the former union boss may have been buried in Milford Township, about 30 miles west of Detroit.
"There have been a number of leads out in this area that have been covered previously in the last 30 years," said Roberts, who has held his post for the last two years. "This is the best lead I've seen come across in the Hoffa investigation."
As for further details, Roberts said the affidavit was sealed, and "unfortunately, I'm not going to be able to give you the answers that you want."
He added that the FBI would not hold another briefing for reporters until agents found something significant. He estimated that agents would be on the property for about two weeks.
The property owners, who have been cooperative, did not own the property when Hoffa disappeared, Roberts said.
An informant reported seeing a backhoe and other "suspicious activity" around the farm on the night Hoffa disappeared in 1975, a law enforcement official said Thursday.
That tip triggered Wednesday's search for Hoffa's remains at the farm.
The tipster said the backhoe was operating near a barn that organized crime members used for meetings, a law enforcement official familiar with the search said.
The informant said that the night after Hoffa disappeared, the mobsters never went back to that area of the farm, according to the official.
Police had received the information several years ago, but verified it only recently, said the official, who asked for anonymity because the investigation is ongoing.
"This is probably a fairly credible lead," Roberts told reporters Thursday.
Aerial footage from the scene on Wednesday showed at least 15 people outside a barn, most of whom were digging a rectangular hole. (Watch the mystery of Hoffa's disappearance -- 2:04)
FBI agents were back at the site Thursday, and investigators were seen pushing metal rods into a field, creating a grid and marking areas where the rods might have struck something underneath the soil.
John and Deb Koskovich have lived on a neighboring property since 1985. When they saw the men digging next door Wednesday, John Koskovich asked them what they were doing. "They just said they were executing a search warrant," Deb Koskovich said.
John Koskovich said there have been reports over the years that Hoffa may be buried in the area, but "we just thought it was just another one of those crazy rumors."
Hoffa was last seen at Machus Red Fox restaurant in Bloomfield Township. He was reportedly there to meet Detroit mob street enforcer Anthony Giacalone and New Jersey Teamsters official Anthony Provenzano. (Who is Jimmy Hoffa?)
Hoffa believed Giacalone had set up the meeting to help settle a feud between Hoffa and Provenzano, but Hoffa was the only one who showed up for the meeting, according to the FBI.
Giacalone and Provenzano later told the FBI that no meeting had been scheduled.
The FBI said Hoffa's disappearance could have been linked to the union boss' efforts to regain power in the Teamsters after he was released from prison.
After serving time for jury tampering and fraud at a federal penitentiary in Lewisburg, Pennsylvania, Hoffa was pardoned by President Richard Nixon on December 23, 1971.
Nixon included in the pardon a condition that Hoffa "not engage in direct or indirect management of any labor organization" until at least March 1980.
Hoffa was 62 at the time of his disappearance.
In September 2001, the FBI found DNA that linked Hoffa to a car that agents suspected was used in his disappearance, but they couldn't prove it.
In May 2004, authorities in Oakland County, Michigan, removed floorboards from a Detroit home and found blood that they thought might be linked to Hoffa's 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.
Investigators ruled blood found in the house was not Hoffa's. The FBI has a sample of his DNA.
Sheehan, who was considered a confidant of Hoffa's, died in December 2003. Provenzano died in 1988 after being convicted in another murder case and Giacalone died of kidney failure in 2002 at age 82.
Hoffa's son, James P. Hoffa, is the current president of the Teamsters.
CNN's Kelli Arena, Kevin Bohn and David Mattingly contributed to this report.