Terrifying moment brave cop's bullet bounces off armoured Dallas gunman - who then shoots the officer in the back before executing him at point-blank range

This is the horrifying moment a brave police officer attempted to take down one of the Dallas attackers by surprise - only for the maniac to shrug off the bullet, turn around and execute him. The footage, filmed from a balcony on a building opposite the shoot-out shows one of the two Dallas gunmen hiding behind a pillar when a cop approaches him from behind. The stealthy officer then attempts to stop the rampage with a well-placed bullet to the shooter's back - but it apparently bounces off, leaving the killer unharmed and the cop exposed.