It's a rather fine point but, in fact, you are wrong. "Thou shall not kill" is correct.
Umm, actually, it's sort of in between.
"Slay" would be a good translation of ratsach, but it is never used in the sense that a soldier slays a combattant; its usage waas restricted to the non-combat killing of another human being. "Harag" is an unrelated word which is used for combat-related killing. The words are non-interchangeable.
You are wrong. I am talking about the translation from Hebrew, not some KJV or other Christian text. http://www.jewfaq.org/10.htm
The NET Bible translator notes for "murder", in Exodus 20:13
The verb jXr (rasah) refers to the premeditated or accidental taking of the life of another human being; it includes any unauthorized killing (it is used for the punishment of a murderer, but that would not be included in the prohibition). This commandment teaches the sanctity of all human life. See J. H. Yoder, “Exodus 20,13: ‘Thou Shalt Not Kill’,” Int 34 (1980): 394-99; and A. Phillips, “Another Look at Murder,” JJS 28 (1977): 105-26.