Judicial process is a subset of due process. You'll notice the comment I was responding to mentioned judicial process. If a US citizen takes up arms with an enemy whom the US is at war with, then the process which he is due does not extend past accurate sighting before the trigger is pulled.

Of course it's a tragedy if a citizen is killed in time of war if it turns out they were not actually engaged in combat alongside the enemy, but war is tragic in general.