So this is something i been contemplating for a while. I'm running into a problem where i can't figure out how to identify if a criminal in a D&D type RPG is able to cast spells. and also if said criminal is a caster, how do you imprison them ethically?

Edit.................. Ok thanks for all the reply's guys. but i am noticing the nobody is addressing my first issue. how do you identify the person in question as a caster in the first place? obviously if the person used magic to commit the crime in the first place their is no need but what if you don't know the criminal is a magic user? and once in prison how do you keep them from teaching other inmates spells in exchange for help with their escape/riot? do you have to have your own separate prison just for casters? is any of this economically feasible? would this make the greatest episode of super jail ever? (sorry not sorry)