A silver Mercedes swings into the passing lane when a machine gun opens fire, sending the car smashing into a taxi, whose terrified occupants scatter. Moments later on the video, posted on the Internet and apparently recorded in Iraq, a white sedan is riddled with bullets as it accelerates on an open highway. Framed as if on a movie screen by the outline of a sport-utility vehicle’s rear window, those scenes and others show what appear to be private security contractors firing on Iraqi civilians. Full Story