The informant who is spurring the search for Jimmy Hoffa's remains is an ailing prison inmate who recently passed a polygraph exam in the probe, says a government investigator who is familiar with the FBI operation in Michigan.

The informant, Donovan Wells, 75, remembers "suspicious activity" on what is now called Hidden Dreams Farm in Milford Township, Mich., at the time Hoffa disappeared, the investigator said Friday.

The investigator spoke on condition of anonymity because some of the information he was relating comes from records that have been ordered sealed by a federal judge. Among them is an FBI affidavit detailing the basis for the search warrant used to dig up the ground on the horse farm.

On the day Hoffa vanished, the property was owned by Hoffa associate Rolland McMaster, according to Oakland County, Mich., property records. McMaster's attorney says FBI agents visited the 93-year-old retired Teamster this week.

Hoffa was last seen on July 30, 1975, at the Machus Red Fox Restaurant about 20 miles from the farm, which McMaster owned throughout the 1970s.

As one example of the account Wells is telling the FBI, the investigator said Wells remembers seeing a number of cars on the property at the time Hoffa vanished, and then a short time later the cars were gone.

The information does not involve an eyewitness to the disappearance or a killing, said the investigator.

Regarding Wells and the recent lie detector test, authorities think he believes the story he's telling, the investigator added.

The Detroit Free Press first reported Wells' identity Thursday night.

Wells pleaded guilty in 2003 to one count of conspiracy to distribute and to possess with intent to distribute marijuana, according to records in U.S. District Court in Detroit. He was accused of being part of a drug-trafficking ring and arranging for a truck to transport hundreds of pounds of marijuana from Texas to Michigan. On Jan. 15, 2004, he was sentenced to 120 months in prison.

According to a U.S. Bureau of Prisons Internet site, Wells has been housed at the Federal Medical Center in Lexington, Ky. The site says his projected release date is Dec. 27, 2012.

In a motion in 2003 for a reduced sentence, Wells' attorney said he had a heart attack in 1994, was diagnosed with prostate cancer in 1997, suffered three strokes in 2002 and underwent a quadruple bypass in January 2003.

The motion described him as "significantly overweight" at 5-foot-9, 290 pounds, and said he was taking nine medications.

He was born on June 17, 1930, and his last address was in Walled Lake, Mich.

At the horse farm, the FBI is bringing in cadaver dogs, demolition experts, archaeologists and anthropologists and suggested investigators might remove a barn.

Able Demolition in Shelby Township is on standby as FBI agents "work their way toward the barn," said Wendy Sitek, an officer manager at Able.

Scientists who have conducted similar searches said they have many tools at their disposal, including ground-penetrating radar and electromagnetic surveying devices along with shovels and probing devices. But unless they have a precise location, their task can be arduous.

"It is extremely difficult to find buried bodies," said William Bass, professor emeritus of forensic anthropology at the University of Tennessee and an expert on human decomposition. "I hope they find him but the experience I've had is people will tell you there's a body out there, but trying to find it is like a needle in a haystack."

Earlier, a law enforcement official in Washington said the latest search was based on information developed several years ago and verified more recently.

Organized crime members had used a barn on the horse farm for meetings, but the location was never used again after the day Hoffa vanished, the official said.

The farm, about 30 miles northwest of Detroit, has three barns and 43 horse stalls on 65 acres of fields and woods.

"This is the best lead I've seen come across in the Hoffa investigation," said FBI agent Daniel Roberts, who has run the Detroit field office for two years.

McMaster's lawyer, Mayer Morganroth, said he doubted the FBI would find anything. He confirmed that FBI officials visited McMaster at his home near Fenton, Mich., and asked about his Hidden Dreams farm.

Morganroth said McMaster was in Indiana on union business at the time of Hoffa's disappearance, and that to his knowledge, his client was never a suspect.

For three decades, the disappearance has spawned endless theories about the former Teamsters boss's demise.

On July 30, 1975, Hoffa was supposed to meet with New Jersey Teamsters boss and Mafia figure Anthony Provenzano and Detroit Mafia captain Anthony Giacalone at the Machus Red Fox Restaurant. Provenzano and Giacalone are dead.

Investigators have long suspected Hoffa was killed by the mob to keep him from reclaiming the Teamsters presidency after he got out of prison for jury tampering and fraud.

In 2003, authorities searched beneath a backyard pool a few hours north of Detroit but turned up nothing. The following year, they pulled up the floorboards on a Detroit home and found bloodstains, but the blood was not Hoffa's.