Forensics, philosophy are a good mix for ‘CSI’

When the going gets tough, Gil Grissom gets philosophical.

On tonight’s “CSI: Crime Scene Investigation” (9 p.m., CBS), when Grissom (William Petersen) and Warrick Brown (Gary Dourdan) arrive at a burglary scene, they are shocked to discover the mummified corpse of an elderly woman locked in a closet, the abandoned remains of a previous crime.

“Sun Tzu once said, ‘If you wait by the river long enough, the bodies of your enemies will float by,’ ” Grissom says, quoting the Chinese military mastermind. “But those,” he adds with delicious irony, “were brutal times.”

The CSI team will need much more than patience and humor to catch a brutal killer on tonight’s show, a gritty and sad episode that shows off TV’s top-rated series in top form. Ken Fink directs from a script by Naren Shankar and Sarah Goldfinger.

Across town, Nick Stokes (George Eads) and Sara Sidle (Jorja Fox) are called to a house to investigate a reported break-in that left a teen-age girl injured, and they find evidence eerily similar to Grissom’s case.

Meanwhile, Catherine Willows (Marg Helgenberger) tackles the bizarre case of a young suburban boy who shot himself in the foot with a .32-caliber Baretta he found in his yard.

The episode features two remarkable guest performances: Stephen Root (the dim, eccentric station owner from “News Radio”) is heartbreaking as the teenage girl’s guilt-ridden father, and Vince Vieluf has a hilarious scene as the older victim’s pothead nephew.

In the end, the CSI team proves once again to be a clever army in the war against crime, but the evidence is increasingly clear: They are not going to win every battle.