Laurence Fishburne joins the cast of “CSI” (8 p.m., CBS) as a professor and renowned criminal pathologist Dr. Raymond Langston. He gets the attention of Gil Grissom (William Petersen) when he invites his class to participate in a “conversation” with serial killer Nathan Haskell (Bill Irwin) via a two-way camera feed between prison and the university. Grissom “audits” the class to gain insight into a current case that may be linked to Haskell’s work.

Not only does this episode welcome Langston, but Grissom makes it official, telling his whole team that he’s finally leaving. Grissom drops the bomb with no emotion and his co-workers react in complete silence.

And who watches “CSI” for the emotional moments? Tonight, we watch a man get strangled, stuffed in a garbage bag and dumped into a ravine. Then we’re given a time-lapse peek at his body’s decomposition, with gaseous eruptions and insect-enhanced decay. When discovered sometime later, the remains are so soggy that Grissom alerts his team with the phrase, “Soup to Go!” Bon appetit.