Quirrell asserts Voldemort slaughtered an entire monastery rather than simply impersonate an appropriate student.
I think we were supposed to read that as:
Riddle attended as an appropriate student, and then came back as Voldemort to indulge in some fun retribution (and possibly to keep others from learning his secrets)
What Vladimir_Nesov said. Notably:
I think we were supposed to read that as:
Riddle attended as an appropriate student, and then came back as Voldemort to indulge in some fun retribution (and possibly to keep others from learning his secrets)