All of that is possible: that the killer is aggrieved at early-morning fitness as a movement or the company and not just MB.
If we are going to zoom out and look at new possibilities, one of the most disturbing is that we are dealing with a calculated serial killer not directly connected to MB, who will move on to other targets in the future. [shudder]
I think it was going to be a mass shooting ( of the people in the exercise group). And, for some reason it was aborted. No specific reason for the church or the people, other than that there was a LOT of info about times and sessions online. Maybe someone(s) who is on fb a LOT. Hope LE checked out the kids who were absent from high school that day. The eerie calmness while inside the church could be drug related. It is one of the strangest aspects of this case. jmo