What is the line in which excessive force becomes murder? or even manslaughter?

An Army official said a soldier had been convicted of using excessive force when he shot dead a prisoner who was throwing stones at him.

He was thrown out of the army but did not go to jail.

If a police officer beat someone to death while interogating him, would he do jail time? If I beat someone to death cause they cut me off in traffic, would I do jail time?

I believe that if these crimes go unpunished, then you are no better than Saddam...