Nearly 40 years after his disappearance, former Teamsters boss Jimmy Hoffa, pictured circa 1955, remains among America's most famous missing persons. Authorities have been searching for the once powerful union boss since he vanished in 1975. The FBI said at the time that Hoffa's disappearance could have been linked to his efforts to regain power in the Teamsters after his release from prison. The hunt continues as police are set to drill in suburban Detroit on Friday, September 28. 
Hoffa slumps in a chair at the Teamsters union office. He was one of the most powerful union leaders in America until being forced out of the organized labor movement. He went to prison in 1967 for jury tampering and fraud before being pardoned four years later. 
Hoffa appears at the Teamsters union convention in 1957, the year he first became union president. 
Hoffa, center, stands with other officials at the Teamsters convention, where he made a successful bid for control of the union in 1957. 
Hoffa testifies at a Senate Rackets Committee hearing in 1958. 
Hoffa on the phone at an airport in 1959. 
An office for Teamsters union local chapters that Hoffa set up. 
Hoffa eats with union leader Joseph Curran, left, in 1959. 
Hoffa holds a Teamsters rally at Madison Square Garden in New York in 1960. 
Hoffa leads supporters at a Teamsters convention in 1959. 
The Teamsters boss appears on the cover of Life magazine on May 18, 1959. The headline reads, "A National Threat: Hoffa's Teamsters; Part 1: Sources of a Union's Uncurbed Power." 
Hoffa, pictured circa 1960, was a powerful labor leader at a time when unions wielded a great deal of sway over elections and were notoriously tied to organized crime. 
From left, "Meet the Press" moderator Ned Brooks, Lawrence K. Spivak and Hoffa appear at an NBC studio. 
Hoffa and his son, James Phillip, enter a federal courtroom in July 1964. His son is the current president of the Teamsters. 
Hoffa, second row, center, leaves court after being found guilty of jury tampering in 1964. 
Hoffa at the Pittsburgh airport in 1971 on his way back to federal prison after being let out to visit his ailing wife. He was released from prison later that year on the condition he not resume union activity before 1980. 
Hoffa poses for a picture on July 24, 1975, less than a week before his disappearance. He was 62 at the time. 
A Bloomfield Township, Michigan, police officer stands beside Hoffa's car after the former labor leader's disappearance in July 1975. Hoffa was last seen at a restaurant in suburban Detroit on July 30, 1975. 
Police sweep a field in Waterford Township, Michigan, in search of Hoffa's body in July 1975. 
Demolition workers in 2006 tear down a horse barn for the FBI in a search for Hoffa's remains in Milford, Michigan. The FBI had received a tip that Hoffa was buried on the farm. 
Police are set to take soil core samples at this Roseville, Michigan, house in the hunt for Hoffa. Police call a tip about a body being buried there around the same time as Hoffa's disappearance credible. The tipster did not claim it was Hoffa's body, authorities say. 
- The author of a book on Hoffa says a tipster, who is a former gambler, contacted him
- The tipster told police that a body was buried at a home about the time of Hoffa's disappearance
- Crews will take a core sample and test it for human remains
- Former Teamsters leader Hoffa disappeared in 1975
(CNN) -- Police will drill outside a suburban Detroit residence Friday in the search for Jimmy Hoffa, the labor strongman whose disappearance is one of the most notorious and mysterious in U.S. history.
A tipster told police that a body was buried at the spot in Roseville, Michigan, around the same time the Teamsters boss disappeared in 1975.
The tipster did not claim it was Hoffa's body, authorities said.
Police Chief James Berlin told CNN on Thursday that while the tipster's information seems credible, he's not convinced the body is Hoffa's because of the timeline. He spoke with the tipster on August 22 and says he believes the person did see a burial.
2010: Digging into the Hoffa legend?
Jimmy Hoffa search picks up at new site The tipster did not come forward sooner out of fear, Berlin said.
Dan Moldea, author of "The Hoffa Wars," told CNN the tipster, a former gambler, contacted him on March 30. The tipster used to do business with a man who had ties to Anthony Giacalone, an organized crime figure who was supposed to meet Hoffa the day he disappeared, Moldea said.
"I am very skeptical," Moldea said of the planned dig. If Hoffa's burial had taken place at the spot, it would have been in full view of the neighborhood, the author argued.
And if Hoffa's body was disposed of, it would have been done in a way that no evidence would be left years later, he said.
At 10 a.m. Friday, crews will begin digging, Chief Berlin said. It shouldn't take long to get a sample, which will be sent to Michigan State University for analysis, CNN affiliate WXYZ reported.
The reading will determine whether there are human remains at the site but will not identify them, Berlin said.
"It took us a while to get the proper equipment to do what we're going to do. If this is a person, they've been down there for 35 years. What's a few more days?" he said.
Results from the soil testing should be available next week, the chief told CNN on Wednesday.
"If they are positive, we will then start excavating," Berlin said.
The alleged burial site is under a concrete slab, and the residence is occupied by new homeowners, who've been "cooperative and excellent to police," Berlin said.
The FBI in Detroit had no comment on the planned search, and a statement from the International Brotherhood of Teamsters said the Hoffa family had nothing to say at this time.
"The Hoffa family does not respond every time a tip is received by authorities. The FBI keeps the family informed and they will have no comment until there is a reason to comment," the statement said.
Hoffa remains among America's most famous, and in many ways infamous, missing people. His presumed death has vexed investigators for almost four decades.
One of the most powerful union leaders at a time that unions wielded a great deal of sway over elections -- and were notoriously tied to organized crime -- Hoffa was forced out of the organized labor movement when he was sent to prison in 1967.
He served time for jury tampering and fraud at a federal penitentiary in Lewisburg, Pennsylvania, until being pardoned by President Richard Nixon on December 23, 1971 -- on the condition that he not try to get back into the union movement before 1980.
Two weeks before Hoffa's disappearance in 1975, federal investigators discovered that hundreds of millions of dollars had been stolen from the Teamsters' largest pension fund, Time magazine points out in its list of the top 10 most famous disappearances.
Hoffa, then 62, was last seen on July 30, 1975, at Machus Red Fox restaurant in suburban Detroit. He was there ostensibly to meet with reputed Detroit Mafia street enforcer Giacalone and Anthony Provenzano, chief of a Teamsters local in New Jersey, who was later convicted in a murder case. Both men have since died.
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 at the time that the disappearance could have been linked to Hoffa's efforts to regain power in the Teamsters and to the mob's influence over the union's pension funds.
Police and the FBI have searched for Hoffa intermittently ever since.
In September 2001, the FBI found DNA that linked Hoffa to a car that agents suspected was used in his disappearance.
In 2004, authorities removed floorboards from a Detroit home to look for traces of blood, as former Teamsters official Frank Sheeran claimed in a biography that he had shot Hoffa. Sheeran had died in 2003.
Investigators ruled that blood found in the house was not Hoffa's. The FBI has a sample of his DNA from a hairbrush.
Two years later, the FBI razed a horse barn in Michigan following what it called "a fairly credible lead."
But the disappearance remains unsolved.
Urban lore long suggested that Hoffa was buried around the end zone at the former Giants Stadium in New Jersey.
As TruTV puts it, the mystery surrounding Hoffa is not simply a "whodunnit."
"The likely suspects are all known, and their motives are well documented. The question is: Where? What exactly did they do to Jimmy Hoffa, and where did they dispose of his body?"
But over the years, numerous theories have been floated. In 1987, Joe Franco -- a former Hoffa strong-arm -- and a New York Times reporter published "Hoffa's Man," which Fortune described as "the hair-raising inside story of Jimmy Hoffa."
"Rather than being kidnapped by rival union forces as law enforcement authorities have long speculated, Franco says Hoffa was abducted by two federal agents," Fortune reported. "He thinks they drove Hoffa to a nearby airport, took off in a small plane, and pushed him out over one of the Great Lakes. Franco says he did not tell federal investigators this bizarre, and unverifiable, story because they would not grant him immunity."
Hoffa's son, James P. Hoffa, is the current president of the Teamsters.
CNN's Chuck Johnston and Stephanie Gallman contributed to this report.
