If I were so rich that I'd never have to work again, I'd go to law school and become a public defender. I can't become Batman, but I can still help others.
I have always thought if I became super rich I would pay for a bunch of people's lawyers to force the government's hand. Essentially the only way our legal system (in the US) "works" is via plea deals. If every case went to trial things would grind to a halt. However, even if a person is innocent they may not have the money to fight the charges or risk the consequences of fighting and losing anyway.
So basically fund defenses until the prosecutors and cops stop being lazy and actually do a justice instead of just a prosecution.