Frank, ---none of us will ever have such evidence. What might such "evidence" consist of? Videotape of an exchange of money? It's a package of actions that represent a common objective of predation in which all that's needed to precipitate mutually supportive statements, policy, is a commonality of interest, of point of view.
Circumstantial is IT.
But a hell of a lot of citizens are in the slam on circumstantial evidence far less convincing.

Capitalism searches out the darkest corners of human potential, and mainlines them.