1:59pm UK, Tuesday June 12, 2012
Brothers John and Clarence Anglin and fellow prisoner Frank Morris pulled off the great escape on June 11, 1962, and to this day remain wanted by authorities as their bodies have never been found.
The Anglins' two younger sisters, Marie Widner and Mearl Taylor, visited the former prison on Monday to commemorate the anniversary of their siblings' daring getaway.
Marie, 76, said: "I’ve always believed they made it and I haven’t changed my mind about that."
Before the prison closed in March 1963, 36 inmates attempted to escape, but only the Anglin brothers and Morris managed to remain elusive to the authorities.
The trio were all serving sentences for bank robbery, but it was the Anglins' history of previous escapes coupled with a failed attempt to sneak Clarence out of federal prison in Leavenworth, Kansas that got them sent to Alcatraz in 1960 and 1961.
Their sister Mearl said: "Just because they did this mischievous stuff growing up, they were not bad boys. They never caused no problems with the family.
"They just got out and did this mischievous stuff until it got to the bank robbery and that's when they really got into trouble. I’m proud of them."
The men’s infamous escape has been made into a book and the 1979 Clint Eastwood film Escape from Alcatraz, in which he played the character of Morris.
The US Marshals Service took over the manhunt from the Federal Bureau of Investigation in 1978.
US Marshal Michael Dyke inherited the case in 2003 and while it remains unknown for certain whether they survived the treacherous bay crossing from the rock to San Francisco, he gets tips every couple of months about reported sightings of the trio.
He said the most convincing clues have included that the Anglin’s mother for several years received flowers without a card and that the brothers attended her 1973 funeral disguised in women’s clothes despite a swarm of FBI agents.
If the Anglins or Morris were ever tracked down Marshal Dyke said that he would still arrest them, but added: "I'd have to compliment them because it was very meticulous what they did, how they escaped from here."
The warrants on them will expire when each man passes his 100th birthday.
US Marshal Michael Dyke insists he would still arrest the men if found
They reportedly spent months using spoons and forks to dig holes in the crumbling masonry surrounding the air vents in their cells, eventually piercing the six and a half inch (16.5cm) thick walls, before squeezing out through roof vents.
In preparation for the escape they also produced a raft and life vests out of more than 50 cotton raincoats that inmates were assigned.
They made mannequin heads out of paper paint and hair acquired from the prison’s barbers, which they left in their beds when they worked on the raft and on the night of their getaway.
Replicas of the dummy heads still lie in their former cells, which are popular stops with the more than a million tourists who visit Alcatraz Island every year.
Alcatraz Island is located in the San Francisco Bay, approximately 1.5 miles (2.4km) from the shore of San Francisco and was a federal prison from 1933 until 1963 for "desperate or irredeemable individuals".
Alcatraz Island from where the men made their great escape on 11 June 1962