Well I have this theory before the seven names list of Jane. So I guess (or guessed because he is not on the list) that could be Walter Mashburn for some reasons, one of then is when Red John (on the episode 1x11 Red John's friends) kill Jared Renfrew and Juana Porfiria Braga and Jared leaves writs "he is Mar " could be one "s" in the end, so could be "he is Mashburn".
He stays friend of Jane, is rich and have many possibilities because he had contacts very powerfuls and he "cath" Lisbon for know that Jane likes her but the principal prove for me is the messenge "He is Mar "