i would say also important to remember, sinai is still very far from the hub of isis leadership, while militants have pledged to isis, it does not mean that they're necessarily coordinating attacks together. u.s. intelligence officials still examining all angles of this disaster. of pentagon correspondent barbara starr has more. >> good morning, to under score what clarissa said, u.s. officials very cautious, saying nothing is definitive. but this is a direction that they're looking at heavily. and a u.s. official telling cnn, and a quote directly, saying, quote, there is a definite feeling it was an explosive device la device plants in lug avenue or somewhere on the plane." why are they saying this? they have reason to believe,