How did Dumbledore know Tom Riddle had opened the Chamber of Secrets before?

[Pearlofthestars]

I've read all of the books, I just can't quite remember the answer..my boyfriend is currently reading all the books and has asked me, and I can't remember. In the Chamber of Secrets, Dumbledore says that he knows, or suspected that Tom Riddle had opened the Chamber of Secrets way back when he was in school, and if so, then why didn't he say anything when they pinned it on Hagrid and expelled him? That wasn't fair to Hagrid. I want to say that I remember there being some sort of explanation to this, I just can't quite be sure from memory. If you know, please refer me to where in the book, page numbers even if you can find the answer to this question, so I can clearly answer him. Thanks.

 

[HPWombat]

Dumbledore suspected Tom Riddle before, but had no evidence. The boy was charming and the other teachers believed him, so Dumbledore couldn't just accuse him just because he had a bad gut feeling about it.

Hagrid, on the other hand, was well known for handling illegal beasts and creatures, and a well-respected student (Tom) had his word against him. Not to mention that he was already looked down on for being a half-human. Dumbledore was already stretching his luck with allowing Hagrid to join when many wizarding parents considered a half-giant too dangerous to teach.

In the end, there's more evidence against him than there is against Tom Riddle.

 

[BreannaStep]

Cause he's the shit!

 

[Camille]

Dumbledore was just badass like that.