CSI: NY Season 7 Episode 18 (04/01/11)
Jo's daughter Ellie was a witness to the crime. She had been on the subway and out of school because she wanted to visit her biological mother. Jo hadn't told Ellie her mother was in jail, but decided it was time to tell her the truth.
A female con artist disguised as an old man was killed on the subway. Witnesses reported hearing a gun shot, but there was no bullet and the entrance to the wound was frozen. Further investigation determined that the weapon was a specialized diving knife. A palm print and trace led the CSIs to the killer who had been conned by the woman and recognized her trough her disguise.