There was a distinct body-hitting-the-ground-with-a-thuddish sort of sound.
“Thank you for taking care of that, Quirinus,” said Dumbledore to Professor Quirrell, who was now standing above and behind the unconscious forms of the three Aurors. “I confess I am still feeling a bit peaky. Though I shall handle the Memory Charms myself.”
However, both McGonagall and Snape know that Harry has developed a charm which can affect the behavior of Dementors:
Albus nodded grimly. “Unfortunately there is now another wizard who laughs at impossibilities. A wizard who, not long ago, developed a new and powerful Charm which could have blinded the Dementors to Bellatrix Black’s escape.
Isn’t Harry’s destruction of a dementor public knowledge at Hogwarts
Edit: Oops, missed it.
Only Quirrel and Dumbledore know of it, since even the three accompanying Aurors were False-Memory-Charmed.
We don’t know what the cover story was that Dumbledore thought up to justify the lost Dementor.
« And so remained only Harry, Professor Quirrell, Headmaster Dumbledore, and an Auror trio.
It would have been better to get rid of the trio first, but Harry couldn’t think of a good way to do that.» from chapter 45
Harry ensured that very few people saw him destroying it.
I believe that the Auror trio was memory charmed.
-Chapter 46
However, both McGonagall and Snape know that Harry has developed a charm which can affect the behavior of Dementors:
-Chapter 61