Complex sentence: According to witnesses two gunmen entered the bar one with an automatic rifle and the other with a hand gun, and the gunman with the rifle just shot at anything that moved in the bar while terrified patrons scrambled for cover.
Split into simpler sentences: According to witnesses two gunmen entered the bar, one with an automatic rifle and the other with a hand gun. The gunman with the rifle shot at anything that moved in the bar, while terrified patrons scrambled for cover.