If it was intentional or it was extreme negligence (i.e. drunk driving), they go to jail. Their punishment is that they killed another human being. That alone is enough to haunt them. So keep them off the streets and keep them thinking about their crime until they get it. If someone broke into my house, I would use force, up to lethal force, to protect myself, but there's a difference between self-defence (and defence of property) and vigilante justice.
Accidental or in a circumstance where they felt great remorse? I wouldn't press charges. Though that's difficult to tell, as the sort of people that kill often are so sociopathic that lying comes easily.
I don't believe in ruining others lives just because they impacted or ruined mine unintentionally. It's not efficient, it's not right, and it's not fair. I'm an atheist, but I thought
this story was amazing.
There's a tenet of some forms of Buddhism that those that we see as criminals or those who make bad decisions are not fundamentally evil - they are ignorant about the consequences of their actions. Sometimes this ignorance is born out of personal irresponsibility, but we as a society have to take credit for part of it. If someone has a mental disorder and kills another, we should have seen the signs and got that person help. You can't fix crime, but rehabilitation, education, and programs like those that exist in prison are part of the solution. Killing people is not.
Oh, and speaking of ignorance:
Capital punishment is a good way of balancing things out: a bad person kills a good person and the bad person forfeits his life as a result. Not only that but it ensures the bad persons DNA can no longer pollute the gene pool.
Yes, because clearly there's a gene for killing people. You probably shouldn't post this sort of thing if you don't know anything about sociology or genetics.