While several well-known criminals, such as Al Capone, George "Machine-Gun" Kelly, Alvin Karpis (the first "Public Enemy #1"), and Arthur "Doc" Barker did time on Alcatraz, most of the 1,576 prisoners incarcerated there were not well-known gangsters, but prisoners who refused to conform to the rules and regulations at other Federal institutions, who were considered violent and dangerous, or who were considered escape risks. Alcatraz served as the prison system's prison - if a man did not behave at another institution, he could be sent to Alcatraz, where the highly structured, monotonous daily routine was designed to teach an inmate to follow rules and regulations.
At Alcatraz, a prisoner had four rights: food, clothing, shelter, and medical care. Everything else was a privilege that had to be earned. Some privileges a prisoner could earn included working, corresponding with and having visits from family members, access to the prison library, and recreational activities such as painting and music. Once prison officials felt a man no longer posed a threat and could follow the rules (usually after an average of 5 years on Alcatraz), he could then be transferred back to another Federal prison to finish his sentence and be released.