>> reporter: vice president biden went further in a fiery speech in new hampshire. >> we will follow them to the gates of hell until they are brought to justice. >> reporter: but exactly how or what the u.s. military will do against isis, on that, president obama was vague. >> this is not going to be a one week or one month or six month proposition. >> reporter: an urgent search for the remaining two u.s. and british hostages is being carried out by spy planes and satellites around an isis stronghold in syria. and investigators are scrambling to try and identify the man seen in these two videos, showing the executions of american journalist steven sotloff and james foley. >> i'm back, obama. >> reporter: investigators are looking at isis fighters who make appearances. see how the camera pans and briefly catches a glimpse of one of the isis camera operators and another driving a truck, both