Escape from Alcatraz: Does letter finally solve mystery of prison's most infamous escapees?

A letter has emerged allegedly revealing the fate of three criminals who pulled off a historic escape from Alcatraz and disappeared without a trace more than 40 years ago.

On the night of 11 June 1962, brothers John and Clarence Anglin and fellow inmate Frank Morris pulled off a prison break so daring it went on to inspire Hollywood thriller Escape from Alcatraz, starring Clint Eastwood.

Aided by another prisoner, Allen West, they used saw blades, spoons and a drill over the course of six months to gradually forge an exit through ventilation ducts in their cells.

The men sculpted dummy heads from papier mache and plaster, and piled towels and clothing under their blankets to conceal their absence, before climbing to the roof through a ventilation shaft and making their way down to the shoreline.

They made their getaway on an inflatable raft - never to be seen or heard from again.

One popular theory to have emerged since then is that they never made it back to land, but their bodies were never found in the depths of San Francisco Bay.

Now - almost 46 years on - a letter claiming to be written by John Anglin alleges that they did survive.

It reads: "My name is John Anglin. I escape (sic) 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!

“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.”

The letter - obtained by CBS San Francisco - was allegedly sent to the city's Richmond police station in 2013 and claims that Clarence Anglin died in 2011 and Morris in 2008.

Since the escape, John Anglin is said to have spent many years living in Seattle, followed by an eight-year spell in North Dakota. At the time of writing the letter, he apparently lived in the south of California.

It was tested for fingerprints by the FBI as part of its most recent reopening of the mysterious case, but results were said to be "inconclusive". The agency has previously asserted that the men died after being swept out to the Pacific Ocean.

But back in 2012, US marshal Michael Dyke, who inherited the case in 2003, said he had seen enough evidence to make him wonder if they could be alive.

This included reports that the brothers' mother received flowers without ever a card for several years after their disappearance, and that they attended her funeral in 1973 disguised in women's clothes.

In Alcatraz's 30 years of operation, the brothers and Morris are three of just five criminals to have been unaccounted for following escape attempts, with 23 caught, six shot and killed, and two having drowned.

The prison shut in 1963 due to spiralling costs and the island is now a popular tourist attraction.