The 'thought' behind the question is likely founded on the idea that once a 'Christian' commits a crime, he/she is no longer a Christian. (A JW branded Christian or any other brand of Christian), but the question becomes more complicated when we consider that a "Christian" theoretically is a transformed personality.
So if the person with the transformed personality commits a murder (an illegal, premeditated killing), what's happened to the transformed personality
Another thought on the question. Is there a difference between 'murder' and 'killing'?
I think everyone gets that difference. So since (in theological concepts) YHWH is the giver of life, he therefore has the right to take life. Many of us would not buy that idea, but its implicit in the stoning scenario of Deuteronomy 17 (and. I've heard elders explaining that a disfellowshipping is like that ), and also in the genocidal invasion of other people's homelands committed in the mythical Jewish invasion of the promised land. But since, YHWH has the right to take life, the stone throwers and the Jewish soldiers with swords killing babies are not murderers or killers, but executioners.
Semantics of course, but part of the reason I was disfellowshipped.