Hebrew has two words for killing. One implies a guilty mind and the other does not. Ask a Hebrew scholar and they'll tell you that the word used for "murder" doesn't include things like military service or capital punishment. And of course, any other interpretation would be at odds with what actually happens in the rest of the Bible.
It is utterly forbidden to kill in the bible.
200 years after Christ, the Roman army was "Christian".
Hmm.