actually the actor Rory Cochrane decided to leave the show, he didn't like the being away from Home for so long and what he called a ground hog affect. getting up and going to work, going Home to bett then back to work, he just didn't like it. link
Lost Son Season 3 Episode 03:01 He Left because he was Home sick and he felt as if he wasn't in the spotlight enough like eric and calligh and Horatio but I realy think he was great he is a Great Actor i hope to see him in a movie(Lost Son Season 3 Episode 03:01)