Why is Grissom leaving CSI?

I believe that William Peterson has said in the past that he was going to fulfill his original 7 season contract with CBS, but was then planning to leave the series because of differences over the spin-offs (Peterson was an executive producer of the first CSI, but completely cut out from the spin-offs by CBS). Last season they started cutting back on his screen time because he wanted more time off. Perhaps adding flexability to his schedule has made him change his mind about leaving permently. I hope so, I really like all the characters, but it wouldn't be the same without him.

The writers of CSI have created a situation where Grissom is supposed to take a 4 week sabbatical. But I've read online William Petersen is fed up with the series and wants to leave the show. He has always been really critical of CBS creating the spin-offs Miami and New York just for the cash. Petersen is supposed to have limited appearances this season. He is planning on devoting more time to his theater and film career and his family. It definately won't be the same show without him !

so he is leaving?? it is his choice and i thought the show just want to take him out

The president of CBS answered this question at a recent press conference and Grissom will be back, as William Peterson wanted some time off, so the fill in is just a fill in and not taking William Peterson's place. William has a contract for next season already.