Hm, I would look into the case files and pick and choose based on those profiles. Those like Mr. Freeze I can easily rehabilitate by making joint patents of his tech, allow him to work on cyrogenics, and help him cure the illness of his wife. Basically get them on their feet and basically get them into a position where they don't need to go to crime. Hell, even the DCAU Riddler from the B:TAS continuity went clean until someone triggered him to go after Batman. Hell the Penguin went mostly straight later in the series and was a major source of criminal world information for the Batman.
Then there are those like Scarecrow... well, let's just say pocket dimension prison on an abandoned island and said pocket dimension is designed that if shit goes down, it'll collapse killing everyone in it.
FAN: Discuss various fictional worlds that don't qualify for SF.