The villainous Margaret Moran (aka Peggy)
Margaret Moran aka Peggy Moran (Jeana LaVardera) was a hidden villainess from "Strangled", episode 2.13 of Crossing Jordan (airdate February 3, 2003). In 1964, Peggy was the wife of police detective Jimmy Moran. Jimmy was revealed to be a serial adulterer, having affairs with numerous women, including diner waitress Ruth Carter.
One night, Margaret (having become suspicious of Jimmy) followed him and caught him having sex with Ruth in her car, infuriating her. The confrontation led to Margaret and Ruth getting into an altercation, which ended when Margaret threw Ruth to the ground. This resulted in Ruth hitting her head on the concrete, killing her. Margaret was shocked by Ruth's death, but helped Jimmy cover up the murder to protect his career. To do so, Jimmy and Margaret drove back to the diner with Ruth's body in her car, with Jimmy choking Ruth's corpse with her stockings to make it appear that the Boston Strangler (a serial killer on the loose at the time) was Ruth's killer.
Later on, though, Margaret became overcome with guilt over her actions. Believing that Margaret would eventually go to the police, Jimmy killed his wife by strangling her with a stocking, staging the scene to look like a copycat killer had murdered Peggy and Ruth. Years later, Boston medical examiner Jordan Cavanaugh, her father Max (who had worked on the case in his days as a detective), and Jordan's boss and co-workers gathered together to re-enact the cold case as part of their yearly ritual and deduced what had transpired. The story was officially confirmed via the blood on a shirt found in the alley where Ruth was killed, which was determined to be Margaret's.