I don't know Redress. When I hear the facts of certain types of cases, I just cannot imagine sympathy for the victim translating easily to some lesser punishment. Also, if your wish is to spare the killer, there'd need to be some sympathy for the killer (though I'm not saying, at all, it necessarily outweighs sympathy for the victim).
I am not sure how what you said here addresses what I said, so I will try and make my point better. If you oppose the death penalty, the most likely reasons are you consider it immoral to kill under those circumstances(ie a defenseless person), or you are concerned about the finality of the death penalty(ie if more evidence comes out, it's too late, and mistakes can and do happen), or some combination of both. Those are not the only possible reasons, but I think that encompasses the reasons most oppose the death penalty.
In the case of the first, the victim is irrelevant to the reason for opposing the death penalty. The concept is that the government simply should not be killing people outside of war, that it is morally wrong. If it is morally wrong, then justice, which should be the goal of a judicial system, is not served by killing some one. While you can feel for the victim of the crime, you cannot undo the crime by killing any one. As far as the criminal, it has nothing to do with sympathy for them. If for example it is wrong to steal, then it is still wrong to steal from a mean, nasty person. If it is wrong for the government to sanction killing in the name of justice, then this is true whether the person is nice or nasty. Morality does not depend on who you are acting towards, but on how you act.
In the second case, the goal is to not dispense injustice. The person holds to the concept that it is to not execute a guilty person than to execute an innocent man. Again, there is no sympathy for the guilty, only concern for the innocent. In both cases, it is easy to justify that society is protected equally well by life in prison as by execution, as is the victim.
I used the torture example in my earlier post, and I think that helps make it clear. If you feel that torture is morally or legally wrong, then this is true even if the person in question is totally vile. I do not care about his well being, I care about doing what is right, even when that is not easy. I feel no sympathy whatsoever for those we waterboarded. Hell, I hope it hurt like hell and made their life hell. I still do not think we should have done it as it is morally wrong to torture.