Jesus told Peter to put his sword up not throw it away. He also had allowed Peter to carry his sword with him as he had it on his person. God was not against killing in all instances. He even sent his people in to posses the land knowing it would result in blood shed. He sent King Saul on a quest to destroy every man, woman, child, and animal in one kingdom. Saul fell out of God's favor for not killing all the rams and bringing back the King. So thou shall not kill must not be taken with such a narrow interpretation to be applied to all things in all situations. God is the same yesterday, today and forever more. He changes not. Some may want to ignore the old testament but it is a schoolmaster that lets us understand the nature of God. Jesus never destroyed the law he fulfilled it. He also never changed the nature of God. Paul refered to the old scriptures in his writing and said that with out the law he would not have known sin.