'CSI' Finale: Treat Williams' Old Case Reveals Corrupt Past (Exclusive Video)

CSI is going back in time for the season closer.

The CSIs dust off an old mob case that took place 25 years ago, bringing former Sheriff's Deputy Sam Bishop (Treat Williams) back into the fold, after they discover a connection to a present-day crime. That decades-old case centered on the murder of a 12-year-old and naturally, D.B. Russell (Ted Danson) and Julie Finlay (Elisabeth Shue) turn to Sam for insight.

The Hollywood Reporter exclusively debuts a scene between the trio wherein a handcuffed Sam gets released after investigators failed to find a murder weapon incriminating him in the case. "What they did find was very interesting," D.B. says. "You're one of us." It's then Sam reveals how he even got into the criminology field in the late 1980s: volunteered, had a knack for science.

Julie explains how Sam got into his current dilemma (i.e., arrested); it was a fingerprint found on a torn photograph recovered at the crime scene the evening before. "Can you figure that one out?" Julie asks. "I retired years ago. Maybe you should figure that out," Sam fires back. But Sam didn't leave his post on good terms. Turns out, he was let go for "insubordination," which Sam refutes.

"I found evidence that was inconvenient for Sheriff Combs. Quickest way to bury my evidence was to bury me," he says. But why was Sam's evidence "inconvenient" all those years ago? Watch the scene above.

CSI wraps up season 14 on Wednesday at 10 p.m. on CBS.

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