FILE – In this May 6, 2010 file photo, Stephen Mara, of Quattro M Securities, works on the floor of the New York Stock Exchange, in New York. If U.S. authorities are correct, Navinder Singh Sarao, helped set off the flash crash that day, raising fears that its not just big banks and hedge funds that can create chaos on exchanges and wipe out the savings of ordinary investors. (AP Photo/Henny Ray Abrams, File)
