A thing about religious (and other) people and the illusion of free will

[Ahriman]

Here's a hypothetical.  Let's suppose a man is arrested and convicted because he's a serial arsonist.  When he was free, he couldn't afford health insurance, but now that he's in prison, he has access to good medical services.  They discover that he had a brain tumor, and that but for that tumor, he wouldn't have started those fires.  Unfortunately, the damage is done, and though they now know the cause, they can't reverse the damage -- the damage which is causing him to light fires.  So he was a serial arsonist through no fault of his own, yet now he is an arsonist likely to re-offend regardless.  Do you make him serve out his sentence?  Do you try to rehabilitate him, only to fail because no amount of therapy will fix his brain?  Or do you lock him up and throw away the key because you know that he is a danger to his community, even though he made no choice that resulted in his becoming one?

How would they ever be able to determine that it was actually the brain tumor the guy had that caused him to set stuff on fire?