I'm sure Steve Centanni knows there is no way the US will release prisoners incarcerated here, but he was forced to make that propaganda video anyway, just as Jill Carroll was. I suspect they were taken captive by a group that is ignorant of US policy, and they really believe the US will exchange them.
I can't remember the US being involved in any sort of prisoner exchanges since the return of Nicolas Daniloff from the Soviet Union in 1986 on trumped up espionage charges, in exchange for a Russian spy.
"I suspect they were taken captive by a group that is ignorant of US policy..."
Yah, I agree that they're ignorant of our policy, but the one thing we know is: they need money. They'll take it from us or from Hamas, whichever; Hamas might pay them to get out of the way so we (US) don't squish them all into one little oily spot on the map of Gaza. We could do it. Or we could get Sauds to do it, for us, undercover-like. That would be rich.