It was one of the most ingenious prison breaks of all time—if it worked. In 1962, inmates and bank robbers Frank Morris and John and Clarence Anglin vanished from Alcatraz, the federal island penitentiary off the coast of San Francisco. They had used sharpened spoons to bore through the prison walls, left papier-maché dummies in their beds and floated away on a raft made from 50 raincoats.

But what happened next has stumped historians for decades. Their bodies were never recovered, leaving many wondering whether they perished in the choppy San Francisco Bay or made it to shore—and freedom.

In the years since nearly six decades of silence from the men led many to conclude that the escape had met a watery end. The FBI closed its case in 1979, concluding that the escapees were unlikely to have survived a treacherous swim of more than a mile of frigid waters to the mainland.

In January of 2018, CBS San Francisco published an extract of a letter addressed to the FBI that told an altogether different story—and claimed that the criminals had been at large since the 1960s. “My name is John Anglin,” it read. “I escape[d] from Alcatraz in June 1962 with my brother Clarence and Frank Morris. I’m 83 years old and in bad shape. I have cancer. Yes, we all made it that night but barely!”

The letter was sent to the San Francisco Police Department’s Richmond station in 2013, the broadcaster reported but had been kept under wraps during a long investigation. An FBI laboratory examined the letter for fingerprints and DNA and analyzed the handwriting within, but the results were inconclusive. “So that means yes, and it means no, so this leaves everything in limbo,” security analyst Jeff Harp told CBS.

In the letter, the writer explained that he was the last living member of the trio, with his co-conspirators dying in 2005 and 2008. He offered a deal: If authorities announced on television that he would receive a single one-year jail sentence, in which he could have the medical treatment he needed, “I will write back to let you know exactly where I am. This is no joke…” The FBI did no such thing and instead repressed the letter.

Though this is the first time anyone purporting to be one of the men has contacted authorities, it isn’t the first piece of evidence that suggests they might have made it out in one piece. Robert Checchi, an officer with the San Francisco police, reported seeing what he described as a “pristine white boat” out in the Bay on the night of the men’s disappearance. It had no lights on, but appeared to have someone on board shining a flashlight into the water. Police followed up on the sighting, but couldn’t find the owner of this strange boat—or where it went next.

More recently, a 2015 HISTORY special showed an alleged photograph of the brothers, taken in Brazil some 13 years after their disappearance. Family members of the men have also reported strange experiences that suggest there may be more to the story than many believe. “It’s always been talked about through the family,” David Widner, a nephew of John and Clarence Anglin, told CBS. “My grandmother received roses for several years after the escape.” If Anglin is still alive today, he would be nearly 90. He has not been heard from since.

Widner expressed dismay that authorities had not contacted the family about his relative’s alleged illness. “For him to say he had cancer and was dying, I feel like they should have at least reached out to the family and let them know [the letter] existed,” he said.

Federal authorities have been quick to quash any rumors of a successful great escape. In an interview with CBS San Francisco, the U.S. Marshals investigating the case told the broadcaster they considered the lead closed with no merit and a simple hoax from someone hoping to scam and embarrass federal and local authorities. “The Federal Bureau of Prisons say that they drowned once they got off of Alcatraz and their bodies were swept out to the Pacific Ocean—end of story,” National Park Service Ranger John Cantwell said.

The prison was closed permanently in 1963, a year after the men vanished. Today, it plays host to more than a million tourists each year, often drawn to the site by the story of the Anglin brothers, which was adapted for the screen in the 1979 film Escape From Alcatraz. John Anglin’s cell, where the men made their exit, is a popular attraction. It’s preserved almost perfectly, with the same gaping hole in its teal-painted wall—but even the scene of the crime offers few answers as to where these great escapees wound up.