Dale Landers, the drummer in the band "Particle Equation", was the boyfriend of the victim, Sonya Gilbert, in Beckett's first case back after being shot. The security system in Sonya's apartment clearly recorded the two of them entering, and its next activity was just prior to his solo exit. Dale even points a gun at Beckett when she comes to arrest him; a double mistake, as it increases the potential number of charges against him, and heightens every protective instinct the team, and particularly Castle, have.