You start with an assumption that he was a trained sniper. I doubt that. Certainly, a trained sniper could have done the job, but many others could have done it as well. You do not need to be a trained sniper to accomplish this crime at the ranges involved and the time available. As an Engineer, he received Basic Rifle Marksmanship in Basic Training. He probably had additional training before he deployed to Afghanistan. That training may or may not have been sufficient, but we don’t know what additional practice/training he did.
Speculation like this will not lead to a conclusion that there were multiple shooters. Evidence will lead to that and according to the Governor, the Mayor, and the Police Chief, such evidence has not yet been found.
Agree. It was also reported (no link, sorry) somewhere that he’d been doing further training at some black gym/gun/martial arts club.
I would be surprised if he could have pulled this off without additional practice after leaving the army. It’s been well over a year since he got out. His skills and focus seemed fresh.