AS if “CSI” wasn’t de pressing enough, to night’s episode is devoted entirely to the disillusionment of Sara Sidle.

It’s the long-awaited episode in which sourpuss Sara (Jorja Fox) makes her exit from the show - finally.

Fox had been rumored to be on the way out last season when it seemed as if her character would not survive being pinned under a car in the cliff- hanging final episode following an “accident” engineered by the serial murderer known as “the miniature killer.”

But Fox didn’t show up to film the episode, amid reports that she was unhappy with having her character killed off. Other reports indicated her walkout may have arisen out of a dispute over money.

Whatever the case, when the eighth season of “CSI” began in September, Fox was back in the role of Sidle, who survived the attempt on her life.

Her return to the “CSI” fold has turned out to be short-lived, however, and tonight (9 p.m. on CBS/2) she frowns her way through two cases and then stalks out of the office for the last time.

She has apparently grown sick and tired of all the blood, guts and rotting corpses with which she comes in contact everyday.

She has also come to the realization that human beings will continue to murder each other in heinous ways no matter how many killers the CSIs put behind bars.

Her sense of futility is fueled by the return tonight of a teen-aged boy (Douglas Smith) and his younger sister (Juliette Goglia) who figured in a previous murder investigation in Season Six and who are now involved in another one.

She doesn’t share her feelings with her colleagues until the end of the episode, when she leaves a note for Grissom (Bill Peterson), with whom she’d been involved.

The show concludes with him reading it, while Fox is heard reciting it for our benefit.

Her voice is so dull, monotone and cheerless that it borders on catatonia. It is excruciating to listen to - like fingernails on a blackboard - but at least it illustrates how hopeless she had become.

Perhaps her exit is all for the better, since the last thing a group of murder investigators needs is a Gloomy Gus among them who no longer thinks the job is any fun.