Batman’s Melvin

I have a question for the Batman experts out there. One of the main arguments against the no kill rule is that the criminals will just continue to commit crime once they’re free again. In the Daredevil comics there’s a character called Gladiator/Melvin Potter who started off as a villain but was rehabilitated and became an ally of daredevil. This helps prove that even villains can be redeemed and supports the no kill rule. I was wondering if there was a similar character in Batman that gets redeemed and helps vindicate his point against killing.