By Eric Cox HIGHLAND PARK, Ill. (Reuters) -Six people were killed and at least two dozen were injured when an apparent rooftop gunman opened fire at a Fourth of July parade in the wealthy Chicago suburb of Highland Park on Monday, officials said, sending panicked spectators fleeing from the scene. Officials told a news conference that six people were killed and 24 taken to hospital, and that a rifle was recovered from the scene. Police were searching for a white male, believed to be about 18 to 20 years old, and asked the public for tips to help find him. Police said initial reports suggested …