Cluesfrom book two
Hagrid mentions that people believe the DADA position is cursed
Peeves breaks the vanishing cabinet which ends up in the room of requirement in bookfive and used by Malfoy in book six.
BOOK 2
The trio are talking about Riddle's award for services to the school and Ron says that meybe he killed myrtle.
Hermione, in defence of Hagrid being the one who released the monster says that maybe it was a different monster attacking people.
After talking with Aragog, Hary thinks that the monster in the shool sounds like a Voldemort kind of monster. Even other monsters don't mention it by name.
There is mention of Tom's long fingers and high, almost unnatural laugh.