John the Methodist has an excellent linguistic look at the proper translation of the 6th commandment. Is it "You shall not kill" or "You shall not murder?" John chose the latter (as do I) and backs it up well.
John is also hosting a discussion on whether it is appropriate for Christians to support capital punishment. I really don't have time to write a full dissertation on the subject, but suffice it to say that I don't have a spiritual problem with capital punishment.
Look, God himself directly proscribed capital punishment for any number of crimes in the Old Testament. God's nature is eternal. It can't be absolutely morally wrong now, if God built a whole legal system on it then. That doesn't work theologically. "The coming of Jesus changed everything" doesn't work for me either. I've read the letter to the churches in Revelations too many times to see Jesus as the eternal doormat of love.
That said, I think there are very good and practical reasons to oppose capital punishment. I understand why people would prefer life imprisonment based on the cost to benefit ratio to society. I'm also concerned with the amount of circumstantial evidence that is used in modern murder cases. All those concerns aside, I still want to fry Mumia.