It's the end of an era on CSI. The Las Vegas Crime Lab is losing the head man. Gil Grissom is packing up his office and leaving Las Vegas. The night shift supervisor, the most influential scientist on the staff, Dr. Gilbert "Gil" Grissom will be a character that won't easily be forgotten, let alone replaced.

If Laurence Fishburne is wise, he'll work with the producers and writers to make Raymond Langston a very different kind of leader.

Looking back at the Grissom years, there are distinctive beats that William Petersen brought to the character and the show. To me, there are six reasons why Grissom will be hard to replace.