Looking at this, not from trying to figure out why, because I'll get to that, but who and how. If you look at the layout of where it happened, as best as anyone can determine now, there was a clear line of sight from where they think the shooter was. 200 yards straight down from a several story building, into a courtyard that was probably recessed another 20 feet.
This wasn't some amateur like the guy who took a shot at Trump. I think that the fact there was one shot says that. Whoever it was, definitely a pro. You'd need to be highly trained to make that shot. I don't think this was a civilian at all. It just doesn't fit the profile.
Why can't they find them or what happened? It seems like whoever did it had it well rehearsed, because they left no evidence behind, no gun or shell casings anyone is aware of. I'll go out on a limb and say it's possible they even had a plan to direct attention towards the other two suspects who got detained.
Whoever it was who did it, I don't think they were in it for attention or anything strictly political. Nobody would want to claim responsibility, but I don't think that doing this is about politics strictly. It just seems very strange. They worked alone, evaded being caught, and with that known, I don't think they would leave much of a trail to follow. Even the pictures and video of somebody on the roof, you can't really see anything. So if that was even the person, they can't even get a description. No height, weight, etc.
Just looking at it, this feels professional. If it was political only or out of rage, I think somebody would have been clouded by anger, had lapses in judgement, made mistakes, etc. Somebody wanted this guy dead for some reason. It just seems too cold, too calculated to have been revenge or something like that. Looking at recent political assassinations, like Minnesota, they caught the guy pretty quickly. The guy was looney tunes, left evidence, made mistakes, etc. This was in front of a few thousand people in broad daylight, and they didn't catch the shooter?
If the FBI and Utah police are on top of things, they should be looking at airports, bus terminals, any footage of people leaving by car, tracking down license plates, etc. Whoever did it, they would want to put serious distance between the scene and themselves as quickly as possible.
So I guess we'll see.