When George Zimmerman shot and killed unarmed 17-year-old Trayvon Martin in February, Zimmerman -- who considered himself a neighborhood watchman -- almost certainly thought of himself as a "good guy."
In November, 45-year-old Michael David Dunn likely thought he was playing the role of the "good guy" when he confronted a vanload of teenagers for playing their music too loud, then fired nine shots into their vehicle after claiming he saw a shotgun barrel. 17-year-old Jordan Russell David was killed, and neither Jordan nor anyone else in the van had a gun.