Interesting...something to ponder.
FWIW....as far as looking for a 'safe' place to shoot from, there are a kazillion group-o'-trees areas around. Literally. I'm beginning to wonder if it's more than a coincidence that the areas just happen to be near a Michael's in two instances and the 'gate of heaven' in two instances. He/she/it had lots of places to choose from if he's just looking for a group of trees in which he can hide.
Well, "just a group of trees" was probably being too general. You'd want an area where you could get into and out of without being witnessed. If he took his shot outside of a vehicle, this would mean an inconspicuous place to park that's not too far from where he's going to shoot- otherwise he'll have to cross a lot of ground carrying his weapon. If he's got an AR-15 or an M16 from the Army, he could easily break it down into two smaller pieces and stuff it in a bag of some sort, but it would still look kind of suspicious. I'd reckon he picked his spot because it offered him enough seclusion for himself and his vehicle and allowed him to overwatch a good "kill zone" that he was sure to have good targets in.