Source is here.
http://www.tvguide.com/News/Mentalist-Reed-Diamond-1035655.aspx Reed will be on episode 2 (probably Thursday September 29 as the season starts the week before). So we won't have to wait for Franklin and Bash season 2 (assuming they get one). Yay!
Description of the episode for those who can't get the link.
Diamond will play Ray Haffner, a confident CBI supervising agent who runs a tight ship. As we previously reported, Haffner will lead a group of agents assisting Lisbon (Robin Tunney) and her team with the investigation of a personal trainer's murder. Something tells us the CBI may not be big enough for both teams.