So if the two of them were duking it out, the "proof in the pudding" will be the cockpit voice recorder.
Several years ago, an Amtrak crew got in a fight in a locomotive of a moving train ... the issue was one guy was a smoker and the other wasn't. There was no cockpit voice recorder to aid in the investigation however. Railroads are still in the dark ages in many respects.
http://kas.cuadra.com/star/images/nmb/02000SGK.pdf
ONTPax