tonight, new york city is launching a program. basically they're testing this right now in about 27 or so officers. they're testing body cameras. with the hope that the body cameras are going to completely change the game here in terms of finding out when something wrong happe happens. but is it a panacea? rene marsh is out front. >> reporter: this video captures a traffic stop turned foot chase. in florida, an officer's body camera captures the moment he opens fire. [ gunshots ] former nfl player, jermaine greene shot at least four times. police were initially criticized. that's until this video was released. showing greene holding his girlfriend hostage at knifepoint. and ignoring police commands. >> video really does provide justice for -- for victims of abuse. and some studies have shown it