A 22-year-old man in combat gear and a mask opened fire Monday morning at a federal courthouse in Dallas and was killed in an ensuing firefight with police officers, authorities said. Cellphone video of the 8:50 a.m. incident at the Earle Cabell Federal Building captured images of the gunman running along the side of the building, smoke from a short distance and then the suspect running into a parking lot and collapsing.