Fishburne, who has confirmed he’s leaving the show after 2-1/2 seasons, worked hard and pretty successfully to fill the large shoes left by William Petersen, who for nine seasons played lead investigator Dr. Gilbert Grissom.

But a “CSI,” or its role model “Law & Order,” isn’t designed to fully take advantage of the movie-star power that Fishburne brought.

Fishburne got an Oscar nomination for his scary portrayal of Ike Turner in “What’s Love Got to Do With It.” His recent one-man stage show on Thurgood Marshall was filmed for a first-rate movie. He can play good or bad. He’s versatile and skilled.

That’s presumably why, when Petersen was leaving “CSI” and Fishburne became available, CBS said, hey, how can we not give this a shot?

He had to be integrated into the show quickly, and the writers did it in an unusual and rather dark way. Langston was an academic criminologist who inadvertently ended up in a “CSI” investigation, thought he knew more than anyone else and helped steer that first case to a bad outcome.

From that experience, though, he accepted an offer to join “CSI” – a step down in some ways, but a challenge.

That also might describe Fishburne’s own situation. Not many actors of his stature do television series.

Artistically, CBS says the experiment worked. Fishburne has said he loved creating Langston.

But “CSI,” a police “procedural” that every week spins and resolves a mystery, never required all the acting versatility or star luster that Fishburne has brought to other tables.

So the show never really got any ratings bump. The numbers have slipped the past two years, and the 13.5 million viewers it averaged last season is half the audience it drew when it was the No. 1 show on TV in 2002-2003.

That isn’t Fishburne’s fault. The few TV shows that live 10 years all lose viewers by then. Broadcast networks in general are losing audience these days.

So CBS doesn’t consider the Fishburne years a failure. Also, given his other opportunities, it never expected to keep him forever.

But the network does now face an interesting set of considerations as it seeks his replacement – particularly since Marg Helgenberger, the other half of the original team with Grissom, says she’s only doing “a few episodes” this season.

So there will be some reinvention – even if you skip the joke about Charlie Sheen being available and already having an ID card for the CBS cafeteria.

Some fans are suggesting, or wishing, that Petersen return. That seems like a long shot.

Whoever it is, in any case, may take the show to the finish line – and doesn’t have to be a movie star.