Lens: A telephoto. Because if I were to save him, he would get a grip on the longer, tele, lens. If again, I don't or cannot, I can get a better ("Pulitzer-prize") close-up.
My spontaneous reaction would be to save him: a) I probably couldn't watch a live being die, without doing smthing
b) saved, he can stand a bog-standard trial. I'd hate for him to benefit from the old paradox: "kill one man and you're a murderer. Kill 1000, and you become a hero".
As with Sean, you had me reading to end, though! :)