You know why many think he is from the military? Army teaches people to be physically organized, to rapidly gather their stuff. Maybe what we view as mental IQ is his good physical organization.
I have a close ex military relative (UK) and he had the ability to react very quickly and effectively to whatever difficulties he faced, but he also didn't go into any situation unprepared. He also wouldn't have taken on more than he knew he could control, unless it was an emergency.
This would suggest BG planned for virtually every scenario. I don't believe many women went to the trail alone, so he was likely to face at least two or three women. He needed to know he could control everyone, which brings us back to the possibility he had a gun.
He then needed to move them down a steep bank and a fair distance. I believe he pre-prepared an area for either the kill, the bodies or both. He needed them to move as quickly and quietly as possible and he must have also been anxious as to whether other people were near or even at these prepared spots. He was under enormous pressure.
I'm not sure every single ex-military person would be able to cope with this. If he is ex-military, it suggests he was in for a fair time and he was specifically trained and skilled at being out in the field and responsible for himself and I suspect others.
The time period he had seems to have been tight, particularly if the girls did fight him, fell over etc. If he's ex-military, he'd have coped with that. But, would his control over himself remain when he's got the girls where he wants them?
We don't know if he did everything he wanted to, or if he ran out of time. How much of the elation (which I'm assuming he felt) was dissipated by the time constraints? He knew he wasn't safe until he was safely away. I think this is important as to whether he will kill again. His mission to hunt/kill without being caught was successful, but was the actual hurt/kill bit a success? Perhaps one or both girls were a specific target, so he doesn't need or want to do this again.It's quite possible he's got this out his system.
Alternatively he messed up, he didn't control the situation, he had very little time and he was seen, filmed and a tape recording of his voice was made. Plus, potentially the police/FBI have some form of DNA. He screwed up like an amateur. Maybe that's why he's ex-military. He was great at the planning and a failure at the engagement. He's a loser. Or maybe the nearest he's come to war is being in a queue to buy toilet roll during the last few months and camping in his parent's garden as a kid.