Rosenberg isn't checking anyone, for some reason.
Speer was a Voltigor. I don't know who killed him.
I think Toxa was being protected, but his attacker also had a defense active. Although, I can't be sure.
Thorium looks like someone from the marines, yes, but I don't think he's a machine gunner.
The notes are really interesting; we can draw some conclusions from them.