I have known of many "jailhouse repentances." But I don't know a single person who learned the religion in jail and kept it when he got out.
One young man came home full of determination to stay on track. It meant so much to his Witness mother. Less than a year. Then again. Poor mom...
They mean well, most of them. But if you're in jail and the only thing going on is your "bible study," well, the conductor has a captive audience