It might also be possible that even Eliezer hasn’t decided who Mr. Hat-n-Cloak is yet—as he’s mentioned previously, sometimes his fiction “writes itself.” Thus, I suspect that Eliezer will not decide the character’s identity until he advances the story a little more.
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...)
It might also be possible that even Eliezer hasn’t decided who Mr. Hat-n-Cloak is yet—as he’s mentioned previously, sometimes his fiction “writes itself.” Thus, I suspect that Eliezer will not decide the character’s identity until he advances the story a little more.
The famous Schrödinger’s Hat.