They weren't normal criminals; this much she was able to tell by their appearances.
Billie and Willie were journeymen criminals, and both had spent time in jail for a number of offenses, mostly physical in nature.
Unfortunately, his efforts were all too often thwarted by a sympathetic judge or a system that could not find jail space for the numbers of criminals brought before it.
It is defended by forts, and serves as a place of banishment for criminals from Brazil.
Criminals have massive disdain for the law.