Sitting in a parked car with an arsenal of weapons and ammunition, the man who fired on police officers in North Dakota earlier this month chose to use the one gun in his vehicle that was modified with a binary trigger. The device allowed the gun to fire so rapidly that it sounded like an automatic weapon. The July 14 shooting in Fargo, which killed one officer and wounded two others and a civilian, has put a spotlight on the device and other trigger modifications that are a growing concern for law enforcement.