John Tagman is an employee of a candy shop who commits a series of bizarre attacks against women, resulting in at least one death. He is based on serial killer Jeffrey Dahmer.
His crimes include removing a calf muscle from one victim and eating it. He also drills a hole in the skull of another victim and pours hot water into it. The victim in that case survives, but suffers extensive brain damage, to the point that she does not remember her own name.
Detective Robert Goren arranges for Tagman to be arrested on a false charge and released, and then takes him out to lunch after his release to "apologize"; he uses this time with Tagman to profile him while Alexandra Eames searches his apartment. After talking with Tagman, Goren theorizes that his motivation is not to kill, but to create a perfect, submissive partner who will never leave or judge him. Goren knows that Tagman is dangerous, but disagrees with Ron Carver's plan to seek the death penalty against him, preferring that he be imprisoned for life.
Goren and Eames arrest Tagman for kidnapping, and trick him into revealing his guilt. In a moment of conscience, Goren tries to get Tagman to confess so his life will be spared. He tells Tagman that it is only a matter of time before he kills again, and that the only way he can be a good person is to take responsibility for what he did. Tagman bursts into tears and confesses, expressing remorse for his actions. He is subsequently sentenced to life in prison.
Shortly afterward, Tagman is murdered by a fellow inmate while at work in the prison laundry. (CI: "Want")