SPOILER ALERT FOR THE LAST EPISODE "RED BARN", SKIP THIS IF YOU HAVEN'T SEEN IT!!!
We think it's Agent Ray Haffner who is a senior agent and seems shady. He offered Lisbon a job at a private detective in this episode. Lisbon finds out this firm is funded by Visualize and it appears like the job offer is to get her away from the Red John Case and Patrick Jane.
She finds out Ray is a member of visualize and also worked at the barn where the 3 bodies were found. AT THE END (more spoiler!!!!)...
...when Lisbon questioned if Ray worked on Ellis's farm (back in the 80's, at the barn), he didn't really answer the question and then he left.
WE THINK HE MIGHT BE RED JOHN!!!!!!!! AAAAAAAHHH!!!! LOL. :) ...or it's Ben Stiles.