From a modest stucco house in suburban west London, where jetliners roar overhead on their approach to Heathrow Airport, a small-time trader was about to play a hand in one of the most harrowing moments in Wall Street history. Navinder Singh Sarao was as anonymous as they come -- little more than a day trader by the standards of the Street. But on that spring day five years ago, U.S. authorities now say, Sarao helped send ...