Characters Who Have Killed

I've got an idea for a little study, but I need your help. Yes, just like Meatloaf at the Special Olympics, I am asking for the mighty comics bloggers to lend a hand to this poor boy. Now that I've run that into the ground, here's what I'm talking about.

I need to know about heroes who have killed, but have since sworn not to do so again. The death doesn't have to have occurred during their career as a costumed hero, it can have happened during an earlier part of their life (soldier, cop, mugging victim, etc.,). Cassandra Cain would be an example, even though she ended up killing again. In fact, if you could include whether they've kept that vow up until now, I'd appreciate that.

One thing, it needs to have at least been something referenced by the character at some point. What I mean is, Batman and Superman both used to kill criminals, but now they don't (Mostly? Is that time Supes killed 3 Kryptonians in continuity?). What I'm not clear on is the specifics of that change. Was there a point in their books, where each said "I'm not going to kill anymore", or did the writers just change the character at some point with no real explanation provided as to why the character's beliefs about killing had changed. If it's the former, by all means include them. If it's the latter, you can mention them, but I'm not sure that I'll count them.

The vague impression I've got right now is that in American comics, it's pretty much all-or-nothing. Either you don't kill, and never have (Spider-Man), or you killed before you were a "hero", and you continue to do that (Wolverine). In Japanese comics, I've noticed at least a few characters who for various have killed quite a lot at an earlier time in their life, and have since sworn, either to themselves or someone else, not to do so again (Kenshin and Ryoko come to mind quickly).

I may be over-generalizing here, but in manga, characters seem to become somewhat less bloodthirsty, or at least, killing is truly a last resort, only when they can't stop the person otherwise. In comics characters either remain the same, at least within the same version. There seems to be a difference between original (Earth-2?) Batman, and the current one. Barring that, they become more violent. They kill, and that causes a descent into greater darkness. I'd probably put Green Arrow and Colossus into this category. It just doesn't seem that characters go the route of getting less dark.

So any information you have on characters, cultural differences, your opinions based on what I've thrown out here, let's hear it.