Jerry Siskind / AFP - Getty Images file

Jimmy Hoffa and his son, James P. Hoffa, who later also became president of the Teamsters, in a 1971 photo.

Updated at 3:40 p.m. ET: Soil tests indicate that no human remains are buried beneath a shed in Roseville, Mich., where authorities were investigating the possibility that the late Teamsters President Jimmy Hoffa might have been buried, officials said.

Scientists at Michigan State University tested two samples from a home in Roseville, a suburb of Detroit, after an unidentified tipster told authorities that he witnessed a body being buried there the day after Hoffa disappeared in July 1975. 

Those tests came up negative for human remains, Roseville police said Tuesday.

The lead appears to be yet another dead end in the search for Hoffa, who ran the International Brotherhood of Teamsters, the country's biggest labor union, from 1957 to 1971. It joins a long line of false leads that have fueled conspiracy theories for years.

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Investigators and other experts had said that they doubted that Hoffa was at the site.

Andy Arena, the former FBI special agent in charge for Detroit, said that while his "gut feeling is that this person saw something," it defies common sense to believe that the Mafia would have buried the body in broad daylight in a busy suburban area.

"If this guy was standing there watching this, and it was Jimmy Hoffa, he would have been in the hole with him," Arena said.

1976 FBI memo on Jimmy Hoffa's disappearance (.pdf)

Dan Moldea, author of "The Hoffa Wars" and numerous other books on organized crime, also said he "never thought that Hoffa was here, ever."

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Jerry Siskind / AFP - Getty Images file

Jimmy Hoffa and his son, James P. Hoffa, who later also became president of the Teamsters, in a 1971 photo.

The FBI and local police in Michigan plan to take soil samples from the backyard of a house in the Detroit suburb of Roseville on Friday, acting on a dying man's tip that the body of former Teamsters President Jimmy Hoffa might be buried there.

M. Alex Johnson is a reporter for NBC News. Follow him on Twitter and Facebook.

Authorities have chased down hundreds of would-be leads since Hoffa disappeared 37 years ago after he met with two top Mafia operatives at a restaurant in Bloomfield Township, another Detroit suburb, in July 1975. All have led to dead ends, but authorities said this lead could be different.

NBC station WDIV-TV of Detroit reported that an unidentified man who is dying from cancer told Roseville police that he saw men moving a black bag at the garage of the house just hours after Hoffa went missing. Acting on the tip, authorities ran radar tests last week that picked up an image of something buried beneath a cement slab in the backyard.

Roseville Police Chief James Berlin confirmed that investigators had received the tip, telling the Detroit Free Press that "the information seemed credible, so we decided to follow up on it."

The newspaper reported that the house is in the 18700 block of Florida Street in northern Roseville, about 20 miles northeast of Detroit.

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The disappearance of Hoffa — who ran the International Brotherhood of Teamsters, the country's biggest labor union, from 1957 to 1971 — has long fueled conspiracy theories. At various times, his body was posited to have been buried under Giants Stadium in East Rutherford, N.J.; beneath General Motors headquarters at Detroit's Renaissance Center; on a farm in Hartland Township, Mich.; in a field in Milford, Mich.; and even on the grounds of the White House. 

What is known is that Hoffa, who was then 62, was chafing at restrictions on his activity in the Teamsters that President Richard Nixon imposed when he commuted Hoffa's 1967 federal prison sentence for fraud and jury tampering in 1971 (he continued to run the union from his prison cell). On July 30, 1975, Hoffa was scheduled to meet with Anthony "Tony Jack" Giacalone, capo of the Detroit Mafia, and Anthony "Tony Pro" Provenzano, a former Teamsters vice president who was also a captain in the Genovese crime family, at a restaurant called the Machus Red Fox in Bloomfield Township.

In a 1976 "here we stand" memo published several years later, the FBI speculated that Hoffa reluctantly agreed to the meeting to try to smooth over differences with Provenzano and Giacalone, who were reportedly perturbed that Hoffa was trying to get back into the Teamsters' leadership, That, presumably, would have lessened the mob's control over the union.

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"It is believed that the hit, if there was one, would have been approved at very highest levels within the Organized Crime structure," the FBI concluded. "If this be the case, it would tend to lend credence to the evidence that PROVENZANO or certainly someone at his level, both within the Teamsters Union and (Mafia), was responsible."

Read the 1976 FBI memo (.pdf)

Hoffa's body has never been found. Provenzano was later convicted of an unrelated murder and died in 1988; Giacalone, who was imprisoned for tax fraud, died in 2001.

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