The Unusual Suspect (S06E18)

A teenage boy, Marlon, is being prosecuted for a murder of one of his female classmates, Stacey. During his trial, his 12-year-old sister Hannah takes the stand, and admits that she herself murdered Stacey, not Marlon. The "CSI" team is now faced with a strange dilemma - two confessions for the one murder. Collusion seems unlikely. As Hannah is a genius, in high school already, even though her confession sounds convincing, some CSI members suspect that she is making up her confession and could not have physically committed the murder. It now has to be decided who should be prosecuted for the crime. (USA Network)