I think you find it very hard to find serial killers in the military, at least ours. Serial killers are well, serial and have to keep killing to satisfy their need whatever it is, for killing. Our military in general, doesnt offer the opportunities necessary to keep killing. When we leave afghanistan, it drops to zero. And for the vast majority of soldiers, they would not come into contact with anyoen civilian enough to be able to relaibly plan and kill them.
At least, in a 'war zone'/ At a home base, well then they are like Snert's accounts and have their whole area as a potential victim, like anyone else.