The character of Larry has been played سے طرف کی two different actors: Thomas Ian Griffith during season 1 (final appearance in "The Leaving Song") and Kevin Kilner (first appearance in "Like آپ Like an Arsonist").
Why he was replaced was never actually mentioned though..
He moved onto 'The Closer' in 2005 and then 'Cold Case' in 2006. Maybe that was why he was replaced.
