Marg Helgenberger to leave "CSI" at season's end

(CBS) Actress Marg Helgenberger, who has been with "CSI: Crime Scene Investigation" since it began 11 years ago, is quitting at the end of this season.

Pictures: Marg on "CSI"
Pictures: CBS Shows this fall

The 56-year-old Helgenberger, who plays investigator Catherine Willows on the show, told reporters gathered in California for the annual fall TV previews she plans to leave at the end of the upcoming 12th season of what CBS is calling the most watched TV series in the world.

"I was planning on leaving after last season," Helgenberger said, adding that producers talked her into staying for another season so they could better script her exit.

Her planned exit comes just as former "Cheers" actor and co-star of HBO's "Bored to Death" Ted Danson joins the cast. Danson, who replaces Laurence Fisburne, will play CSI supervisor DB Russell. Executive producer Don McGill says Russell is a family man who grew up in a commune with folk-singing parents.

Danson, 63, said he enjoys working on a crime drama, but joked "they still won't give me a gun."