It would depend on several factors:

Why did they kill someone? Self-defense is kosher, but premeditated murder costs a few style points. Reasons for heat-of-the-moment killings come into play, too.
Who did they kill? Was it someone who had it coming, or some poor, innocent schmuck?
Do they have any long-term mental health conditions, or have any present scenarios caused some wiring to otherwise pop loose?
How did they kill the person? Humanely or through long, drawn-out torture?

Overall, probably not, except for self-defense and heat-of-the-moment with good justification, or if they killed someone who truly deserved it.