I was betting Mr. Hat-n-Cloak = Quirelmort. (Remember that after the little scene Harry witnessed, he had to rush off. Perhaps to catch up and meet with Zambini? And the ultimate purpose of this was to arrange for Harry to further mistrust Dumbledore? At least, that was my very first thought, although now I'm thinking there were probably easier ways to accomplish that.)
I was betting Mr. Hat-n-Cloak = Quirelmort.
Snape also seems like a wildcard possibility here - Zabini suspects him, anyway.
(OTOH, Quirrell knew Zabini was a quadruple agent, which could have intrigued him enough to want to see if he could be a quintuple...)
ETA: There is now a third thread, so send new comments there.
Since the first thread has exceeded 500 comments, it seems time for a new one, with Eliezer's just-posted Chapter 33 & 34 to kick things off.
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