The Federal Bureau of Investigation did not find the body of Jimmy Hoffa, the Teamsters union leader last seen on July 30, 1975, during a dig this week on a farm north of Detroit.

The FBI's Detroit field office has calculated the cost of the three-day excavation – which included approximately 40 agents and other resources – but doesn't plan to immediately release the price tag.

"We know the cost of it, but we aren't releasing it," Detroit FBI spokesman Simon Shaykhet told U.S. News in a phone interview.

"To be fair," he added, "all tips that are credible are thoroughly checked and investigated in any investigation."

Shaykhet said the farm's owner will not be financially compensated for the dig, but said "we will have restored the property to its original condition" before it's handed back to the owner.

"We will be leveling the ground and laying down fresh soil and seed," he said, as part of an agreement with the owner.

The tip was evidently provided by Tony Zerilli, 85, a former Detroit mobster who has an online store selling signed photographs of himself for $9.99 and "manuscripts" - promising "the true story once and for all" about Hoffa's death - which cost $7.99 for print copies and $1.99 for electronic ones.

Zerilli launched his website in January, at about the same time he started telling reporters he knew where Hoffa was buried. "I know all about it, [but] I wasn't involved, no way, shape or form," Zerilli told WDIV-TV in January. Zerilli claimed in the interview that Hoffa was buried on a rural property near Adams Road and Orion Road in Oakland County - the location of the FBI's search this week.

The FBI would not confirm that Zerilli was its source, but Zerilli's attorney David Chasnick told U.S. News that his client did provide the tip and then worked with agents for seven or eight months on the case.

"We're obviously disappointed," Chasnick said. The attorney denied Zerilli sought to profit by publicizing a false tip.

"He still believes it's there," Chasnick said. "If there was a way he was going to truly profit, I'm assuming he'd have sold something for $44.95."

According to Chasnick, FBI agents spent months diligently vetting his client's story before acquiring a search warrant for the site.

"They did a lot of leg work on this," he said, "it wasn't just taking his tip and going with it."

Chasnick says FBI agents originally sought to dig up a wider swath of farmland, but that the request was whittled down by a judge.

Agents filed a 70-80 page sealed affidavit when seeking the search warrant, Chasnick said.

"It wasn't a quick little thing... I feel bad for them, because it's a case they wanted solved," he said. "I hate that they didn't do the entire area because it leaves a question mark."

FBI Special Agent in Charge Robert Foley publicly acknowledged the dig's failure during a Wednesday press conference.

"With any investigation we consider cost-benefits analysis," Foley said, according to The Associated Press. But, he added, "the FBI and its partners are no corporations. We do not have a profit margin as a bottom line."

Shaykhet, the FBI spokesman, said he didn't know how many times the FBI has tried to dig up Hoffa's remains.

Other failed FBI searches for Hoffa include a 2006 dig at a farm in Milford, Mich., reportedly involving 40 to 50 FBI agents, a 2009 excavation at a Detroit lumberyard and a 2012 search beneath a Roseville, Mich., driveway.