He was whistleblowing on Deustche bank taking advantage of their shareholders, and in turn is being paid out of a fine that they had to pay (which, of course, comes from the shareholders themselves not the accused execs) so it's a bit of a perverse incentive for him. The rest of us can stand jaw-dropped at turning down a massive sum of money, but bravo to him for pointing this out with his (seemingly selfless) action here.
