Law & Order (1990) : 16x12

After Philip and Valerie Messick are attacked in their home, Green and Fontana follow the trail to a small-time thug named Jay Fleckner. After Valerie's testimony unintentionally helps free Fleckner, he is found dead, and detectives soon realise that Bob Cerullo, a family friend of Valerie and her late husband, was the triggerman. Unfortunately, when McCoy attempts to prosecute Cerullo, a retired cop, he threatens to claim that he deliberately planted evidence in his past cases in an attempt to get McCoy to drop all the charges.