on saturday, fr sharm el sheik. climbing to31,000 feet, then disappeared fromm radar. >> looking at the tail section is very telling. if it came off first, was it a bomb or structural failure? >> reporter: isis quickly claiming responsibility, but some doubt. today, the ex-wif of the pilot said he had repeatedly complained about the state of the plane. russia declared today a national day of mourning. you lose your kids, this grieving mother id, life is finished. those black boxes will be taken back to moscow to try to unlock the mystery. airlines say they will not fly over the sinai peninsula until more is known. >> steve ganyard, could this have been a bomb? >> a bomb could be one of the causes. the problem is, the claims from the terrorist group don't match up with the plane coming apart at 31,000 feet. the other thing to look at,, some sort of structural problem. >> will the black boxes matter? >> well, what's more important, the wreckage on the ground, is there things like bomb residue? the investigation needs