There have been times I felt threatened by a person I assumed to be "un-armed" (but you can never be positive of that point, can you?). Had that person made a furtive move, I might have shot them. That's not the time for hesitation if you suspect your life is at risk.
I haven't read a lot about the case because everything seems so hyperbolic. But, regardless of anything I might read I wasn't there. Maybe it was murder, maybe it was a reaction to a credible perceived threat. Anything more I might say would be speculation and assumption.