In its heyday, it was the ultimate maximum security prison.

Located on a lonely island in the middle of San Francisco Bay, Alcatraz—aka “The Rock”—had held captives since the Civil War. But it was in 1934, the highpoint of a major war on crime, that Alcatraz was re-fortified into the world’s most secure prison. Its eventual inmates included dangerous public enemies like Al Capone, criminals who had a history of escapes, and the occasional odd character like the infamous “Birdman of Alcatraz.”

In the 1930s, Alcatraz was already a forbidding place, surrounded by the cold, rough waters of the Pacific. The redesign included tougher iron bars, a series of strategically positioned guard towers, and strict rules, including a dozen checks a day of the prisoners. Escape seemed near impossible.

Despite the odds, from 1934 until the prison was closed in 1963, 36 men tried 14 separate escapes. Nearly all were caught or didn’t survive the attempt.

The fate of three particular inmates, however, remains a mystery to this day. Here is their story.