3x13 - Blue Murder

When Blair Patterson's beheaded body is found in a van that's been sitting in a neighborhood for days, his wife turns the squad onto Emily Glover, a tenant in the apartment building Blair managed, who immediately confesses to his murder and claims she and Blair were killing couples throughout the city. When another couple is found dead in the same way as the others, the squad realises that something with Emily's story is off, and it's up to Oosterhuis to try to get it out of her as Emily will not talk to a female detective, and has already given up on Weeks.