ATLANTA -- Federal investigators say an Atlanta police helicopter hit the top of power line pole and its support cables before it crashed on a busy city street, killing two officers on board.No one on the ground was injured. The officers were searching for a 9-year-old boy who had run away from home. He was later found unharmed.NTSB investigator Ralph Hicks said Sunday witnesses heard the helicopter and saw a flash of light when it hit the pole. He says part of the chopper's landing gear was caught in the support cables and the power company had to help authorities get it down.Hicks says investigators are trying to figure out why the helicopter crashed. He says they hope to have a preliminary report later this week.