Taking another look at it, it REALLY doesn't look legit because it's supposedly a "Reply to All" misclick, right? Then where's the headers of the email from Buccellato?
Now, maybe someone in his organization betrayed him and forwarded it on to David, who deleted the internal stuff because he didn't want to divulge who snitched. This is possible, but not likely.
My guess is David's just another Anonymous with a grudge.
Any confirmation on how much money Len owes, and to who?