Did I Do Something Illegal?

Alright I have a friend. We'll call him Adam. I was informed Adam has payed people to do some of his schoolwork for him. I asked another person and from what I remember they supported the claim. I told a principal. Now Adam swears it is not true and is furious about this ( he doesn't know I reported him). He he is going to sue when he finds out who did this and has already contacted his lawyer and the police. Then the principal will have to admit I reported it, to the police.If he does sue when he finds out it was me, could I be found guilty of slander or defamation of character? Regardless of whether he is guilty or not, I acted on what I thought to be true. I don't see anything being put on his record or anything and I haven't been telling the world he pays people to do his work for him and if he didn't do it, then I really don't want to get him in trouble for it