Major Crimes season 4 episode 19
Episode title: Hindsight (1)
A young woman and her 3-year-old son are shot to death while driving through gang territory in the wrong colored car, and the gun used in the murder is quickly connected to the most troubling series of unsolved homicides in LAPD history. As Captain Sharon Raydor and the rest of her division attempt to solve the mystery, Amy Sykes begins an uneasy alliance with a disgraced former LAPD detective with a novel theory and a corrupt past.
