It's been 12 years of blood, small fibers and gun powder residue for Marg Helgenberger on 'CSI,' but the time has come for her to say goodbye.

"It's been a fifth of my life, and it's been quite a ride," Helgenberger said in a new 'Entertainment Tonight' video. "How can I leave this? ... It's so much more than a job and that's why it has such an impact on me."

Helgenberger has played Catherine Williows on the CBS series since the series premiered in 2000. She's seen cast members leave only to return -- Jorja Fox -- and welcomed several new castmates, most recently Ted Danson. The cast is optimistic Helgenberger hasn't swabbed her last mouth.

"Every other day I'd make some joke about her staying," Danson said. "I totally get it. Eleven and a half years is a long time and part of you must want to strut your stuff elsewhere."

The case took an ugly turn this week on 'CSI: Crime Scene Investigation' (Wed., 10PM ET on CBS), when the officers found themselves having to take on one of their own. When a fellow cop started utilizing vigilante justice on guilty people who got away with murder, they were faced with an impossible situation.

On the one hand, these people were guilty and probably nobody knows it and feels it more than the officers who worked those cases. So in that regard, he's giving justice to someone who deserves it. But it's also murder, and it's outside the system they're sworn to uphold. But he's one of their own, too, so what do you do?

Amy Sedaris vs. Alan Cumming? We're so there! The 'Strangers With Candy' star is joining CBS's 'The Good Wife' as a nemesis for Cumming's character Eli Gold.

According to TVLine, Sedaris will play Stacie Hall, a lobbyist who starts poaching Eli Gold's clients.

"We love Amy. We sometimes have dreams of switching all the actors from 'The Wire' and 'Strangers With Candy,'" Robert and Michelle King, 'Good Wife' co-creators and executive producers, said in a statement to TVLine. "The next best thing is to have Amy playing Eli Gold's nemesis."

In other casting news ...

'The X Files' star Annabeth Gish is heading to 'CSI.'

According to EW, Gish will star in a three episode arc as a childhood friend from Catherine Willows' (Marge Helgenberger) past. Gish's character, Laura, is married to a billionaire military contractor honcho who is investigated by the CSI team. It turns out he may be involved in an arms theft.

Gish's arc starts with episode nine.

Marg Helgenberger is rumored to be leaving the series after the first 12 episodes, could Gish's character be involved in her character's departure?

In other casting news ...

The lab at 'CSI: Crime Scene Investigation' has been in some very capable hands over the years -- first William Petersen, then Laurence Fishburne and now Ted Danson is taking over the reins.

EW is reporting that Danson will be the drama's leading man for the upcoming 12th season, playing the CSI's grave shift supervisor after transferring from the Portland crime lab.

"You can create a new character on the page, but until the perfect actor comes along and breathes life into it, it's just words," said executive producer Carol Mendelsohn. "We're very excited Ted Danson came along."

After CBS's exhaustive search to find a worthy person to pass the torch to, they actually managed to come up with an intriguing, well-known and likable choice -- and one that we never thought of.

Cop killers get a lot of extra attention in law enforcement, and with good reason. However, on 'CSI: Crime Scene Investigation' (Thu., 9PM on CBS), there's at least the chance that the murderer didn't know the victim was a cop. They probably knew, but the possibility had to be considered.

The victim was incarcerated along with the suspected killer. According to the warden it was a matter of walking a group of the Aryan Brotherhood by a group of black men. Now why you would do this is completely beyond us, unless you want to stir up something.

Ray was suspicious of the warden as well. Why was a former cop even in general population, he asked? But having no official avenue right away in any direction but the gathered criminals, he turned his frustration on them.

Fans of Justin Bieber have been enjoying him all over their televisions the past few weeks. With his movie in theaters, he's been hitting the talk show circuit hard core and he was a big presence (albeit award-snubbed) at the Grammys.

Now, he's back on 'CSI: Crime Scene Investigation' (Thu., 9PM ET on CBS) playing troubled teen Jason McCann.

SPOILER ALERT!!

This is almost definitely the last time you'll see Bieber on the show. After setting a bomb that endangered the team, he was defiant until the end. He tried to get the driver of the van he was pulled over in killed, and then pulled a piece on the hordes of police.