Actually, that part is trivial. It was Trump. 
It’s the intermediate ones who will be, as you say, difficult to pick out of the crowd.
OTOH, one of the features of mobs in general is that they often aren’t really led. Once a group of vaguely like-minded people show up in one location, so called “mob psychology” takes over. Like a more sophisticated version of bird’s flocking behavior, everyone takes their cues from the surrounding people and waves of different behavior, be that violent or peaceful, just spread spontaneously through the crowd.
Which is also why a tiny cadre of agents provocatuers can be so effective. They can deliberately trigger very specific behaviors in the vastly larger crowd by being a critical mass of common behavior in one or two small clusters.
That speaks to the events after the group was assembled and began marching towards the Capitol.
How that particular list of individuals happened to show up that day may be much more amenable to identifying the movers and shakers who made it so. Or maybe not, and the “blame” lies entirely with the amorphous nature of the R.E.T.C.H. :