A third answer might be Quarantine, and certainly death is the ultimate quarantine. I could see it giving a victim some peace of mind to know for sure that an assailant isn't coming back. Death might also be more acutely threatening than captivity as a consequence of a crime. I'm not even sure which I would pick to suffer if given the choice.
That's an interesting answer. I would still personally classify it under punishment, because you are removing someone's right to free movement etc. but i think that's a topic of another, separate debate. I think death only becomes acutely threatening if there is something after it. Because i don't believe that, The only part of death i fear is the pain during the killing act. Because it is the pain I fear, the concept of years, decades of long, drawn out pain is much, much better as a deterrent.
I agree that even if you considered the point of prison to be quarantine, it would still be a punishment. However, if your goal is quarantine rather than punishment, you don't need to choose the solution that maximizes suffering. I disagree that death is only acutely threatening if there is something after it. It depends very much on how highly you value your remaining lifespan. Right now, I'm enjoying life, and I'd be more disappointed about my reduced lifespan than afraid of the transition. This is actually pretty new to me; l I feel like I understand where you're coming from. Not sure what else to say about that. Feelings of solidarity and respect. It's not even clear to me that a life sentence in prison would necessarily be a net negative. I'm sure there would be some suffering, but hedonic adaptation would have your back, and I hear some people get to read a lot.