what are you learning about this investigation? 26 airlines go in and out of this airport, and tonight, several cancellations over concerns about airport security. as officials zero in on this new leading theory of a bomb on board, experts are examining the victims bodies for signs of trama from an explosion or shrapnel. a bomb is the leading theory for u.s. intelligence and british officials tonight. we cannot categorically say why the russian jet crashed, but we have become concerned that the plane may well have been brought down as a result of an explosive device. reporter: all u.k. flights to and from the peninsula vz behavn halted. security has tightened where the doomed russian flight took off. isis has been operating successfully and assassinations