That's what I was thinking, too. It's probably cheaper to campaign with a government aircraft than a chartered one--if I'm not mistaken, campaigners have to refund the government only the price of a first-class commercial ticket when flying on unofficial business.
It's a very rare catch--congrats on getting some great shots of it! It's been mentioned as one of the CIA's rendition aircraft:
http://en.wikipedia.org/wiki/Renditi...596GA.2FN977GA