I'm not in favor of capital punishment, but not for many of the reasons people typically oppose it.
For me, it's more about pragmatic, policy reasons. We know that in our country, the death penalty doesn't deter crime. We've also found that death penalty cases create a lot of media attention, which provide incentives for prosecutors to be more aggressive and decreases the chances that the defendant gets a totally fair trial. We also have some evidence that such penalties are not fairly applied, racially. PLUS, they're all expensive.
In a perfect world, where 100% guilt could be proven , and such an approach would deter crime, I wouldn't have a problem with it, but we clearly don't live in that word. For me, I wouldn't want to accidentally kill somebody, which we've done, under those circumstances. It isn't worth it.
I don't think the rights of a victim are unduly trampled on if their assailant spends the rest of his life in prison.