>> reporter: the urgent search for the remaining two u.s. and other western hostages is being carried out by spy planes and satellites over the isis stronghold of the syrian city of raqqah. this is where u.s. officials believe isis staged its barbaric murders of journalists steven sotloff and james foley. the president vowed isis will pay the price. >> we will not be intimidated. their horrific acts unite us as a country and stiffen the resolve to take the fight against these terrorists. >> reporter: the isis commander abu bakr al-baghdada are key, and so are the masked men in the videos and those not seen are part of the execution and video team. >> those who make the mistake of harming americans learn that well will not forget, our reach is long and justice will be served. >> reporter: in the search for clues, some gruesome isis videos offer unintended leads. here the camera pans and briefly