For decades, it’s been a tantalising mystery.
Did the three prisoners who made a daring, elaborate escape from Alcatraz in 1962 make it out alive?
Brothers John and Clarence Anglin and fellow inmate Frank Morris spent six months constructing their ingenious plan which remains the only successful jailbreak in the prison’s history.
But there’s never been any concrete proof the trio survived their journey off the island fortress via a homemade life raft.
Many believe it most likely they drowned, though no bodies were ever recovered.
Now a handwritten note has emerged which might point towards a more startling reality.
According to TV channel KPIX 5 , it was sent to San Francisco’s Richmond station in 2013.
The FBI confirmed it remains the most recent piece of evidence and forced them to reopen the cold case.
It reads: "My name is John Anglin.
"I escape 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 existence of the note is the latest twist in a case that has fascinated the world for more than 55 years.
Under the leadership of Morris, the inmates secretly spent months tunneling out of their cells via air vents to an unguarded passageway.
When guards did their nightly check, the men filled their beds and placed fake ‘heads’ they’d constructed from soap wax on their pillows.
Climbing to the top of their cell block, they then set up a makeshift workshop.
The raft was assembled from more than stolen 50 raincoats and paddles from scrap wood.
On June 11, 1962, the preparations were ready and the group made their bid for freedom.
A fourth man, Allen West, had been involved in the plot from the start.
But when the time came, he was unable to fit through the hole in his cell wall and by the time he’d widened it the others had left.
He later cooperated fully with police and was not punished for his role.
Meanwhile, the Anglins and Frank Morris then carried their raft down a 50ft vent pipe and scaled two barbed-wire fences while avoiding searchlights and guards.
They used an accordion to inflate their raft and are believed to have set off into the San Francisco Bay at around 10pm.
The note supposedly written by John Anglin, who would be 86 if he were alive, says they spent many years living in Seattle and North Dakota but he now resides in South California.
He said his brother Clarence died in 2008 and Frank Morris three years later.
In the letter, Anglin apparently offers a deal to give himself up in exchange for a promise of only one more year in jail.
The FBI analysed the letter for fingerprints and DNA but the results were inconclusive.
So for now the mystery remains unresolved.