It could be weeks before officials know why Egyptair Flight MS804 vanished from the sky on Thursday morning, with 66 people on board. But French authorities have begun hunting for a cause, including the possibility an explosive device might have been placed on board the Paris-Cairo flight at Charles de Gaulle airport. Egyptian aviation minister Sherif Fathy told reporters on Thursday that “the possibility of having… a terror attack is higher than the possibility of having a technical failure.” Fathy did not say how he had reached that conclusion. French Prime Minister Manuel Valls said in a radio interview early Thursday that his government “cannot rule out any...