If you must lie, be brief

So yesterday I wrote a test, and today I got to find out that the questions leaked two days before the test. How it happened still remains a mystery to me.
The news was everywhere, names were mentioned and some of the names really shocked me as I was not expecting such from them. Anyways, humans are not to be trusted. I do not know what hurt me the most, if it was the fact that some of my friends knew about it and didn't tell me or it was the fact that I didn't know before the test.
I called some of them and asked if the rumors were true and most of them went on and on that they didn't know of any leaked questions and acted surprised while some said they found out five minutes to the test.. wow. I could see the lies through them. I decided to asked the leaker.. lol sorry, the guy that supplied the questions about the whole thing and he confirmed that he gave most of them the questions. Still thinking if I should let them know I know the truth or let the matter die. What do you think?