Three Alcatraz inmates presumed dead after making a daring escape from the island prison more than 50 years ago survived and could still be alive today, their families say.

Brothers John and Clarence Anglin and fellow inmate Frank Morris made it off the island on a makeshift raft in June 1962 and were never seen again, with prison officials insisting they drowned.

But relatives of the Anglins say they have proof the men paddled to shore and survived, which includes signed Christmas cards sent to the brothers' mother and a photograph which they claim is evidence they were alive in the 1970s.

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Brothers John and Clarence Anglin and fellow inmate Frank Morris (left to right, top row how they looked in 1962 and bottom row how they could look now) were presumed dead after fleeing Alcatraz in 1962, but relatives say they have proof that they are still alive

The men fled Alcatraz more than 50 years ago in a makeshift boat made of raincoats

The image, which is yet to be revealed, will be shown in a new History Channel documentary on the escape.

The Anglins and Morris' incredible escape from Alcatraz saw them chisel vent duct openings in their cells with spoons until they were wide enough to fit through.

Before leaving their cells, they left paper-mache heads with their own hair attached in their beds to make it appear like they were tucked up in bed.

They clambered through the vents, broke onto the roof of the jail and made their makeshift raft out of raincoats, which they then inflated using an accordion-like concertina.

The men - who would now be in their 80s - set sail from the north-eastern shore of Alcatraz and were never seen again. The raft was found on the San Francisco coast the next day.

Alcatraz officials and the FBI insisted that the men drowned, with the investigation closed in 1979. They say no one has ever successfully fled from the notorious jail.

The escapees left paper-mache (pictured) heads with their own hair attached in their beds to make it appear that they were tucked up in bed

The Anglins and Morris' incredible escape from Alcatraz saw them chisel vent duct openings in their cells with spoons until they were wide enough to fit through

The Anglins’ nephews David, 48, and Ken Widner, 54, kept quiet about their evidence until now, but want to set the record straight while their mother - the escapees' sister - is still alive.

'[Alcatraz officials] were not willing to say, "Maybe [the escapees] did make it,"' David Widner said. 'That gave me the motive to prove them wrong.'

The family took their claims to investigator Art Roderick, a retired US marshal who worked on the case for 20 years.

The Christmas cards, which arrived in 1962, were verified as legitimate by a handwriting expert, but it is not known when they were written.

The Anglin family also have a photograph which they say suggests the men were alive in the 1970s, and has led investigators to renew searches for the trio in South America.

The Anglins’ nephews Ken (center), 54, and David Widner (right), 48, say they own a photograph, seen by investigator Art Roderick (left) that proves their relatives were alive in the 1970s

Alcatraz officials and the FBI insisted that the men drowned, with the investigation closed in 1979. They say no one has ever successfully fled from the jail. Pictured, an official in Morris' cell in 1962)

Mr Roderick told the New York Post: 'This is absolutely the best actionable lead we’ve had.

'When you work these types of cases there’s a feeling you get when stuff starts to fall into place. I’m getting this feeling now.'

Previously the authorities had claimed bones washed up on the shore of San Francisco in 1963 belonged to one of the escapees, proving their demise.

However the Anglin family allowed investigators to dig up the remains of the brothers' elder sibling Alfred for DNA testing, which later proved the washed up bones were not theirs.

Morris, however, has no surviving relatives so the remains could be his.

Alcatraz: Search for the Truth airs on the History Channel at 9pm EST on Monday.