Oct. 7, 2012 -- After a tip from an informant last month, police in Michigan dug up a driveway in the Detroit suburbs in hopes of finding Jimmy Hoffa's body, only to ultimately come up empty-handed.
But for a few days, the unsolved mystery of Hoffa's disappearance once again captivated the country.
Hoffa, who headed the powerful International Brotherhood of Teamsters Union at one point, was last seen outside a suburban Detroit restaurant in 1975, but his cold case is just one of many involving famous Americans who seemingly vanished without a trace.
Amelia Earhart, the first female aviator to fly across the Atlantic Ocean, disappeared over the Pacific Ocean as she tried to fly around the world in 1937.
D.B. Cooper is the alias given to a man who pulled off the only unsolved airline hijacking in this country's history when, in 1971, he stole $200,000 and then parachuted from the plane, never to be found.
Experts believe that it is a unique combination of fame and mystery that fuels people's fascination with these cases.
"Here are people who were already famous, had a reputation, and then suddenly they disappeared and nobody knows where they are," said Robert Thompson, a pop culture expert and professor at Syracuse University. "If Earhart's story, for instance, wasn't absolutely perfectly structured to have people be continually fascinated by her disappearance for another quarter century, I don't know what was. She's a celebrity who takes off, never arrives at her destination and nobody ever finds her. That's like a Zen-level of dramatic interest."
Dave Paulides, a former police investigator and author of the book, "Missing 411," which deals with unexplained disappearances in the wilds of North America, said that that sense of the unknown only serves to pique people's interest in these figures.
"It's that unknown that pulls at our brain to try to unravel it," he said. "It's the ultimate mystery.
"When you talk about cases like that, there's that thing we grew up with: What's out there in the dark? Don't go too far. Something scary might be out there," he added. "Maybe, in some instances where these people have disappeared, there really is something scary out there."
While both Hoffa and Earhart were prominent figures in their day, the fact that their cases continue to be unsolved has helped continue the public's interest in them.
"What keeps the cultural capital of the likes of Earhart and Hoffa is the fact that these are unsolved mysteries. That's what drives the fascination," said Thompson. "If Hoffa had died a natural death of old age, people who weren't alive when he was would not know him. He would not have remained a household name had it not been for the fact that he disappeared, so his multi-generational visibility is partly due to the fact that he hasn't been found.
"Earhart is different because of who she was," Thompson said. "She might have been someone who would have been talked about in schools and books even if she hasn't gone missing. But even so, when Earhart comes up in conversations, it's usually about the fact that she disappeared."
The specific circumstances surrounding the disappearances of Earhart and Hoffa only heighten the intrigue.
Whereas Earhart's case involved a romantic mystery of vanishing into some unknown space in the skies, Hoffa's case featured the frightening prospect of disappearing in a place that was anything but far-flung or out-of-sight, a development that continues to fascinate Dan Moldea, author of the book, "The Hoffa Wars."
"The thing that's always put the hook in me is the fact that here was an American citizen, well-known, who was snatched from a public place on a crowded street in broad daylight and was never heard from again," Moldea said. "That's not something that's supposed to happen in the United States."
Hoffa's disappearance has a unique level of intrigue because it was not merely about the man himself, but rather it involved a slew of other prominent figures.
"Hoffa is very much a part of lots of conspiracy theories -- the Marilyn Monroe thing, peddling tapes of JFK with a woman," Moldea said. "He was important on so many different levels."
More than three decades later, speculation runs rampant not only about how and why Hoffa disappeared, but where he ultimately ended up. Maybe buried beneath Giants Stadium in New Jersey? Or even dumped in a Florida swamp?
As time goes on, though, the obsession over what happened to Hoffa, Earhart, Cooper and others has started to fade slightly.
"In my generation, Hoffa was a big name," Moldea said. "I'm 62 and we are very familiar with who he was. But I find it remarkable that I'm finding fewer and fewer people who know."
The interest surrounding Cooper, for instance, has faded even faster, Thompson said, because the criminal was not famous before he pulled off his daring plane heist.
"In the cases of Hoffa and Earhart, we knew these people and then they disappeared," he said. "In the case of Cooper, we have created a sense of celebrity after the fact -- and those things tend not to go [multi-]generational."
Even as the legends of Hoffa and Earhart slowly start to wane with each generation, new unsolved mysteries that will become part of the American folklore of the 21st century are sure to arise.
"I think cases like Hoffa and Earhart may go away with time, but new ones will take their place," Paulides said.