A gunman stood up through the sunroof of a Jaguar and fired Tuesday into another car travelling on a U.S. road, killing three men and seriously injuring a fourth, news reports said. A police officer witnessed the shooting in Dallas, Texas, and said the gunman fired an assault rifle. He stopped to help the victims, whose car crashed after the gunfire. The three victims, who were pronounced dead at the scene, ranged in age from 19 to 36. Police said they were investigating whether the shooting was related to an altercation at a nearby bar. --SP 2315 Local Time 2015 GMT