WASHINGTON—Federal investigators trudged through rugged terrain Monday in search of wreckage from a business jet to solve the mystery of why the plane veered off course and slammed into a mountain, killing four people. A day after the plane flew over the nation’s capital, prompting the military to scramble fighter jets, the Federal Aviation Administration…

WASHINGTON—The pilot of a business jet that flew over Washington and crashed in a remote part of Virginia appeared to be slumped over and unresponsive, three U.S. officials said Monday, recounting observations by fighter pilots who intercepted the wayward flight. The revelations came as federal investigators trudged through rugged terrain to reach the site where…