They do it both ways... Sometimes it's just the guy at the top... Sometimes it's a team dispersed throughout the crowd... Sometimes it's like the Michigan "cell" - composed mostly of Feds, that they tricked into going along with a doomed plot, to kidnap Gov. Christine Whitmer...
And sometimes it's just a whole mess of Feds, and whatever few randoms are dumb-enough to get swept up in the rhetoric, and the arrests.