It's extremely complicated. That's not a cop-out, because there are many, many factors. Many people who don't deploy kill themselves. It's clearly not the single factor.
The common factors really are mental illness or a crisis. It can be a crisis with a big C or a little C, because when you're ill you can interpret different kinds of things. There's also the hopelessness and the impulsivity I mentioned, as well as other things.
For some, deployment could be the mediator toward getting mental illness. It's not binary in terms of whether you have deployed or not, it's what happens during that deployment. One person may be in a deployment where they're on the base camp, relatively safe and comfortable. Another person may be outside the wire, facing the bad guys every day. Clearly those two people haven't had the same experience. There are pre-enrolment factors as well—who you are, how you cope with stress and day-to-day things.
I think there are a fair number of things.