Nocturne

S1 E21: A sharp-eyed photo developer puts Detectives Benson (Mariska Hargitay) and Stabler (Christopher Meloni) on the tail of a seemingly harmless piano instructor (guest star Kent Broadhurst) who molests his students -- all boys -- but their prime witness is an unstable young man (guest star Wilson Jermaine Heredia) who recoils when he sees the suspect's videotape of his shame from years before. Even more disturbing for the detectives are more scenes from other tapes that could compromise their case and cause more heartache. Richard Belzer, Dann Florek and Michelle Hurd also star.