That is a good book, though hard to follow in places because of the complexity of Garrison’s case. It’s a difficult task to weave all of the characters and subplots into a readable account. As for “the painter,” I think Allen Dulles is a good a guess as anyone. He had access to all of the major players.
I did read that first part in Miami Magazine. Interesting stuff. There was so much going on behind the scenes, so many people who hated the Kennedy’s and King.