It fully explains his lack of skill in the dictionary attack, and the desperation, and sheds new light on the Quirrell/​Snape forest conversation earlier.
If Quirrell knows that he has Snape as an ally (as Harry lost him given the speculation RE: Lily), and has removed Draco and Hermione from the picture (and he does seem very guilty) this seems like a relatively good time for him to come out of hiding, which also explains his behavior RE: the interrogation.
I find that theory extremely persuasive.
It fully explains his lack of skill in the dictionary attack, and the desperation, and sheds new light on the Quirrell/​Snape forest conversation earlier.
If Quirrell knows that he has Snape as an ally (as Harry lost him given the speculation RE: Lily), and has removed Draco and Hermione from the picture (and he does seem very guilty) this seems like a relatively good time for him to come out of hiding, which also explains his behavior RE: the interrogation.