WASHINGTON, March 15 — A former EgyptAir pilot told American investigators two years ago that the co-pilot of EgyptAir 990 crashed the plane into the Atlantic Ocean to take revenge on a company executive who had just demoted him and was riding as a passenger, a person involved in the investigation said today. American aviation investigators say they do not know whether the explanation given by the pilot, which was first reported today in The Los Angeles Times, is true. Since the crash of the Boeing 767, Egyptian officials have argued that there was no evidence that the co-pilot, Gamil...