Well I know you don't believe in free-will but what I meant by a criminal "changing" is just him regretting his actions and willing not to do them anymore
There needs to be a reason. Punishment is only punishment, it doesn't deter anything or create empathy out of nothingness.
If you tell me that the prisonner saw a girl talking to his dad on the prison phone booth while his daughter refuses to speak to her and he is punished to death.. then yes. HERE is a chance for him to start doing an introspection.
But a punishment is like a spank on a kid's face. (don't do that). If you don't show a way to do things better or to remove the need for the bad aciton to happen, the kid will make the bad action again and thus will not understand the punishment EVEN if deep down, they know it's was not a good action.
Understanding that an action is bad and preventing one self to do an action are two very different things. Most rapist know that rape is bad but they do it anyway. This is why they must aquire a BIGGER understanding of their action and have the tools to make a big introspection.
If you push an introspection on someone too hard, it risk to destroy them and if you threaten to death someone. You will - at best - end up with someone who wanted to change, but didn't have the tools to do it.
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Which can happen in an instant in the sense of, a criminal can sit in his bedroom and decide he doesn't want to anymore
This is not change.
This is a choice.
Choices, as I explained many times, are the results of a long change, not change itself. They are the last brick to transform a person. This can only happen if the person was transformed over time by the material conditions of their existence.