I read that the shooting suspect was an electronics technician. Even if this was his third Iraq tour, not sure why this is as a case of combat stress as electronics technicians don’t normally see combat. Of course, maybe he was the guy who went out into the field to fix things and routinely got shot at. I guess we’ll see.
In an overseas deployment to a war zone, there are other factors besides combat that can lead to stress. Which, of course, does not excuse this person's actions in the least.