SVU, This One Stands Above The Rest

By Season 14, Agent Dana Lewis had worked with the SVU team on a number of cases/episodes, including one wherein she attempted to infiltrate a domestic terrorist organization ("Raw"), and one wherein she was investigating her own rape ("Penetration"). Over time, Lewis developed a friendship built on mutual respect with Mariska Hargitay's Detective Olivia Benson, and proved a worthy foil to the overly self-assured and impulsive Detective Elliot Stabler (Christopher Meloni). 

However, when she returned to the show in "Secrets Exhumed," her sterling reputation was tarnished — and her FBI career and time on the show brought to a dramatic halt — when it was revealed that Lewis murdered her ex-lover's pregnant girlfriend early-on in her law enforcement career, then used her crime scene skills to make it look as though said girlfriend had been the victim of a serial rapist and murderer.

The episode was one of many "ripped from the headlines" storylines, and posited Agent Lewis as the fictional version of real-life killer and detective Stephanie Lazarus. In 2012, Lazarus received 27-years-to-life in prison for murdering her ex-boyfriend's wife, Sherri Rasmussen, back in February of 1986 (via Vanity Fair). In "Secrets Exhumed," Lewis attempts to coax a confession out of serial killer Brian Traymor (Harold Perrineau), but Detective Amaro (Danny Pino) becomes suspicious of her involvement when Lewis doesn't immediately reveal that she was once in a relationship with the cold case victim's boyfriend, Noah Bunning (Jay Karnes). Benson doesn't initially believe Lewis could have been involved (and neither does the audience), but as the evidence against her begins to pile up, she has no choice but to interrogate her long-time friend. In the end, Lewis confesses to murdering her rival in a fit of rage and jealousy, and is arrested.