The correct translation is "Thou shalt not murder" or "Thou shalt not commit murder." However you prefer it. I can even prove this.
Numbers 35:26-27
"But if the slayer shall at any time come without the border of the city of his refuge, whither he was fled;
and the revenger of blood find him without the borders of the city of his refuge, and the revenger of blood kill the slayer; he shall not be guilty of blood:
"
Numbers 35:31
"31 Moreover ye shall take no satisfaction for the life of a murderer, which is guilty of death: but he shall be surely put to death. "
Translation: You can't take stuff in exchange for the murderer's life. He has to die.
Romans 13:4
"For he is the minister of God to thee for good. But if thou do that which is evil, be afraid; for he beareth not the sword in vain: for he is the minister of God, a revenger to [execute] wrath upon him that doeth evil. "
Anyone who thinks you cannot kill, ever, because of "Thou shalt not kill" has been reading rather selectively.