If someone was beating (or raping) a woman without killing her, and you killed that someone to stop them, would that make you a murderer?
Just curious as to your line of thought.
I can answer this on a personal level, but it would not be a legal determination whether I would be a murderer. I can only answer if it would make me right, despite the law.
If a person were beating a woman, without killing her, and I shot him in the head with a gun, that would probably make me a murderer, and would probably make me wrong too. My friend witnessed a woman being beaten by a man, and she broke his arm with a baseball bat. She didn't aim for the head, but the beating stopped immediately. There is a certain principal for matching force at play here. The judge later agreed.
But this was not the case with Moses. Moses believed it was okay to beat slaves. He even gave slave beating guidelines. So that was not the issue. The slave driver was allowed, by law, to beat the slave. Moses agrees with that! Moses held a high station in Egypt. If killing the slave driver was within the realm of acceptable, he could have successfully argued his case. He didn't. He buried the body and ran away, to take up a much lower station, to marry beneath his station, and to leave all behind.
Even today, the cops will ask, "Why did you run?" Hiding evidence of a crime increases the intent and stakes.
So let's go back to your illustration. If I saw a woman being beaten (not to death) and shot the guy in the head, then maybe I have a case. But if I bury the body and then run away, my case kind of fizzles. Why did Moses kill a man for doing what Moses believed was acceptable---beating a slave? Why did he hide it? Why did he run? Because he was a murderer.