Montgomery's Dark Secret
Yes, he was the mystery third cop. Monty, just a rookie at the time, helped two senior officers kidnap mobsters for ransom. Things went awry one night and an FBI agent was killed, leading to a massive cover-up that an enterprising lawyer named Johanna Beckett tried to expose. The captain had been living with a horrible secret for years: that his actions led to the murder of Beckett's mom.