S1·E4 Revenge and Remorse (The Guilty Alibi)

Frank investigates a district judge's courtroom after it is booby-trapped with a powerful explosive. The main suspect is a recently paroled ex-convict with a history of similar bombings. Upon questioning the bomber's ex-wife, Frank and Ed find she's more interested in getting charity than the fact that her ex-husband may be up to his old tricks. Frank and Ed discover the bomber has a showgirl girlfriend on the side. She has the perfect alibi for her boyfriend, but Frank and Ed wonder if she's really just covering for him.