Sean Cavanaugh is the current lieutenant of Boston Police Department's Homicide. He is old friends with Vincent Korsak.
History
Little is known about Sean's past, but it is mentioned by Korsak that Sean lost his wife and son in a fire back when he and Korsak were rookies.
His wife and son died in an explosion, caused by Patrick "Paddy" Doyle (Maura's father), by attempt to kill him, to stop him to investigate the drug deals of an Colombian drug cartel.
According to Korsak, he didn´t have close relationships after the death of his wife.
He has a daughter but not much contact with her. He was never married to his daughter's mother.
Season One
In Season 1 Episode 7 "Born to Run" Cavanaugh mentions that the suspect is his daughter's age.
Season Two
Season Three
Sean dated Angela Rizzoli (Jane's mother) causing much discomfort between the Rizzoli`s and Sean.
Season Four
Sean planned to kill Patrick Doyle in the Court house, after learning that Patrick Doyle was responsible for his family´s death. He was talked out of his plans by Maura, saying that the knowledge of being placed in prison by his true love Hope will be much harder than to bear than being killed by Sean.
Angela broke up with him.