Even though Jimmy Hoffa's remains weren't found during a two-week search at a Michigan horse farm, FBI agents have a message for those responsible for the disappearance of the former Teamsters boss: They'll never stop looking for you.

"The FBI does not give up and will pursue all logical investigations, no matter how much time has passed," Judy Chilen, assistant agent in charge of the FBI's Detroit field office, said Tuesday in announcing the end of the dig at Hidden Dreams Farm.

Agents said they will continue investigating Hoffa's 1975 disappearance, because they still have leads to pursue — despite the fact that their best lead in three decades yielded nothing more than a water line, a beer can and other trash buried beneath a demolished barn.

"There are still prosecutable defendants who are living, and they know who they are," Chilen said.

Over the years, theories have suggested Hoffa was buried at Giants Stadium in the New Jersey Meadowlands or was even ground up and tossed into a Florida swamp.

But no trace of him has ever been found, he was declared legally dead in 1982, and his whereabouts have become a great American mystery.

The search in Oakland County's Milford Township involved 15 to 20 FBI agents from Detroit, Chicago and Washington, as well as five to seven agents guarding the property 24 hours a day. It also included anthropologists, archaeologists, a demolition crew and cadaver-sniffing dogs.

The farm 30 miles northwest of Detroit once was owned by a Hoffa associate and was said to be a mob meeting place before the union leader's disappearance.

Chilen said she believes Hoffa had been buried on the farm and that she had no evidence his body had been moved.

Lou Fischetti, who heads organized crime investigations in the Detroit FBI office, added: "We really don't have any indication that it was or wasn't moved."

Fischetti said that before the barn was destroyed, FBI evidence technicians searched below the farm's surface with rods and high-tech gear, eliminating all of the likely spots for the body to be buried.

Chilen said agents had to remove the barn because structural engineers determined that it would be safer and less costly to demolish it rather than reinforce it and dig under its roof.

"The reason for taking down the barn was safety concerns for the horses as well as the investigators," she said.

The government will pay for the barn to be rebuilt, and for a temporary stable to house about 20 horses displaced by the search. Fischetti said he expected the total cost of the search to be less than a quarter-million dollars.

Hoffa vanished nearly 31 years ago. Investigators long have suspected he was killed by the mob to prevent him from reclaiming the Teamsters presidency after he got out of prison for corruption.

In 2003, authorities excavated beneath a backyard pool a few hours north of Detroit. The following year, police ripped up floorboards in a Detroit home to test bloodstains. The blood was not Hoffa's.

The FBI began the latest excavation May 17 after a tip from Donovan Wells, an ailing federal inmate who once lived on the farm and was acquainted with its former owner, 92-year-old Hoffa associate Rolland McMaster, according to a government investigator.

McMaster's attorney Mayer Morganroth said he was not surprised that the search ended with the mystery unsolved.

"We never expected that anything was there," he said, adding that the FBI probably felt pressured to respond to the tip, lest it seem as if it were not trying to solve the case.

"We want to thank the FBI for their efforts and their continuing resolve to solve this crime of 31 years ago," Hoffa's daughter, Barbara Ann Crancer, a judge in St. Louis, said in a statement issued on behalf of herself and her brother, Teamsters President James P. Hoffa.

"Each time there is an event such as this our family suffers anew the loss of our beloved father, grandfather and great-grandfather. The Teamster members who revere his memory suffer with us," said the statement, which was published in Wednesday editions of the Detroit Free Press.

James Elsman — a lawyer who says Wells told him he saw a grave being dug at the farm in 1976 and heard comments about Hoffa being buried — said Tuesday that Wells is allowing him to share notes of those conversations with the FBI. He said he has a meeting scheduled with the FBI but would not say when.

While many veteran investigators and Hoffa experts were skeptical about the search, little Milford Township seemed to relish the attention. A bakery sold cupcakes with a plastic green hand emerging from chocolate frosting meant to resemble dirt. Other businesses sold Hoffa-inspired T-shirts and put up signs with wisecracks such as "Caution FBI Crossing Ahead."

Hoffa was last seen on July 30, 1975. 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 of whom are now dead.