Alcatraz mystery deepens after discovery of letter signed by fugitive claiming prisoners survived escape

Authorities have never established whether inmates survived daring break-out from notorious island jail

The three Alcatraz escapes remain on the US Marshals Service most wanted list to this day, along with photos of what they may look like now (EPA)

It is one of America's most enduring mysteries, troubling investigators for decades and inspiring Hollywood cinema.

Now a letter has emerged which appears to shed light on the fate of three prisoners who escaped from Alcatraz in 1962.

Authorities have never determined whether brothers John and Clarence Anglin and fellow inmate Frank Morris survived the daring jail break.

The FBI closed its case in 1979, concluding the men were unlikely to have survived the 1.5-mile journey across San Francisco Bay’s frigid waters from the island prison to the mainland.

But no conclusive evidence of the prisoners’ deaths has ever been found, and the US Marshals Service continues to investigate their disappearance to this day.

A letter has now come to light that claims the trio of bank robbers survived their perilous escape and lived into old age.

“My name is John Anglin,” the handwritten missive begins. “I escape from Alcatraz in June 1962... Yes we all made it that night, but barely!”

San Francisco police received the letter in 2013 (KPIX 5)

Anglin’s cell is now a highlight for tourists, who can see the ventilation shaft he squeezed through with his fellow escapees before they floated off from Alcatraz in raft made of raincoats inflated with a concertina. They had spent six months beforehand carving holes with sharpened spoons and stolen saws to crawl into a network of pipes and plumbing so they could evade guards.

The fugitives were never seen again and the FBI said they were likely to have drowned.

However, according to the letter, Morris lived until 2005 and Clarence Anglin died in 2008.

The letter was sent to San Francisco Police Department in 2013 but was not publicly disclosed by the force. The document has come to light five years later after it was obtained by local TV station KPIX 5.

The letter’s writer says he spent years living in Seattle following his escape before moving to North Dakota and Southern California.

He says he is now “83 years old and in bad shape” and tries to strike a bargain with police.

“I have cancer,” the letter reads. “If you announce on TV that I will be promised to first go to jail for no more than a year and get medical attention, I will write back to let you know exactly where I am. This is no joke.”

Alcatraz pictured in 2006 (AFP/Getty)

The letter was passed to an FBI laboratory to be examined for fingerprints, DNA and handwriting. But the results provided few answers.

"Handwriting samples of all three escapees, John Anglin, Clarence Anglin and Frank Morris, were compared to the anonymous letter, and the results were deemed 'inconclusive'," said a statement from the US Marshals Service.

The escapees' family are also undecided about the letter's authenticity.

"I really haven't come to a conclusion whether I believe that it's John reaching out or not," said the Anglin brothers' nephew, David Widner.

But he said he thought his uncles could still be alive, revealing that his grandmother received roses with a card signed with their names for several years after their escape.

"It's always been talked about through the family," added Mr Widner. He also criticised authorities, who never contacted his family about the letter.

"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 it existed," he said.

The three inmates remain on the US Marshals Service watch list, along with photos of what they may look like today.

Their break-out was immortalised in the 1979 film Escape from Alcatraz, starring Clint Eastwood as Morris.

Alcatraz was shut down in 1963, a year after the famous escape.

Although authorities at the time insisted deadly currents meant no one could survive the swim from Alcatraz to the San Francisco shoreline, the route is now regularly tackled by triathletes.