Frank Morris and brothers Clarence and John Anglin, all serving time for bank robbery, vanished from the prison in San Francisco Bay on the night of June 11, 1962.
Although many historians believe they perished in the frigid, treacherous currents surrounding the maximum-security island prison, their bodies were never found and some believe they made it to freedom.
"I always believed they made it, and I haven't changed my mind yet," Clarence and John Anglin's sister, Marie Anglin Widner, said on Monday during a press conference at the prison.
Widner, 76, believes her brothers attended their mother's 1973 funeral dressed as women. The FBI definitely attended.
"If (the authorities) thought they were dead, why keep looking for them?" her son, Dave Anglin, said, adding that his uncles were good swimmers who "used to break the ice in Lake Michigan."
The trio's Houdini-like breakout from the supposedly escape-proof prison spurred the biggest manhunt since the kidnapping of aviator Charles Lindbergh's baby in 1932, and inspired the 1979 Hollywood film "Escape from Alcatraz," starring Clint Eastwood.
Half a century later, the search for clues about the fate of the men continues. Authorities have chased thousands of leads in nearly every state in the union, U.S. Marhsal Michael Dyke said.
Dyke, a history buff who has been looking for the escapees since 2003, still gets tips about the case and said he pursues them all.
He told Reuters he would like to check the DNA of a set of bones that washed ashore at nearby Point Reyes National Seashore in 1963 to see if they could be one of the escapees.
He asked the Anglins' relatives for DNA samples, but so far they have refused, he said. Morris has no known relatives.
Asked what he would say to the escapees if he found them, Dyke said he would tell them, "I'm glad you stayed out on the road for as long as you did, but you have to go to jail now."
If they survived, Morris would be 85, John Anglin would be 82, and Clarence Anglin 81.
The Anglins used a toy pistol to steal $19,000 during a bank robbery, Dave Anglin said.
"They were good, old boys," he said. "They never hurt anyone. They wanted a different life than what they had, and it got them in a lot of trouble."
During the robbery, he said, a woman fainted, and his uncles paused the robbery to get her a drink of water.
The Anglins' sisters and nephews visited the scene of the crime on Monday. They wanted to see for themselves how the escapees used mess-hall spoons to gradually dig a small passageway through concrete walls to a ventilation shaft, how they left papier-mâché heads under their blankets to fool guards, and how they glued 50 raincoats together into a raft.
To mark the anniversary at the prison, now a tourist attraction owned by the National Park Service, the Anglins' relatives also took part in a panel discussion with Dyke, a former prison guard and the daughter of a warden.
Over the years, the mystery has captured the imagination of a public seemingly sympathetic to the villains. Nevertheless, federal marshals vow to pursue Morris and the Anglin brothers until they are arrested, are determined to be dead or turn 99.
U.S. Marshal Don O'Keefe said the investigation "serves as a warning to fugitives that regardless of time, we will continue to look for you and bring you to justice."
Alford Ray Anglin, John and Clarence Anglin's brother and a co-defendant in the bank robbery that sent them to prison, died in 1964 when he touched a high-voltage wire trying to escape from an Alabama jail, according to a news accounts at the time.
Marie Anglin said she visited Alford Anglin in jail shortly before his death, and he told her that he had received a letter from his brothers following their escape from Alcatraz. She believes Alford's jailer's beat him to death when he refused to tell them how to find his brothers.
Dave Anglin said he plans to have Alford body exhumed to try to confirm the cause of his death.
Alcatraz, also referred to as "The Rock," opened as a civilian prison in 1934 to house some of the nation's most incorrigible criminals. Its better-known inmates included Al Capone, George "Machine Gun" Kelly, James "Whitey" Bulger and Robert Stroud, better known as the Birdman of Alcatraz.
The prison was closed in 1963 by then-Attorney General Robert F. Kennedy, citing the high cost of running it and badly needed repairs.
