I'm not sure where you are, but it appears that you are not a native English speaker, which is not a disparaging comment but merely an observation.
Given that, you may not know the legal aspects of your situation. In the United States, for example, the truth is a valid defense against charges of libel or slander, which may be the way your emails were perceived. In other words, if you have proof that the student in question committed the offenses you listed in your emails, then you should by all means take all of that proof with you to your meeting with the university officials. Lay out the proof for them so that you can establish that everything you wrote in your emails is the truth.
Once you have established the veracity of your charges, then you and the university can address the problem of the manner in which you shared those charges. If your intent was to notify the authorities at the university of the man's criminal behavior, then you should have contacted one or two trusted university officials who are in a position to take action against the student in question. If your intent was to warn other students against this student, it might be a good idea, but the way you did this was perhaps less than ideal. Again, notifying the authorities of his bad intent and behavior with an urgent request to have the student disciplined, stripped from a position of authority where he has/had access to the private information of all students, and perhaps expelled was the first step you should have taken.
In that manner, the student would have been called in to face the university, would have had the opportunity to respond to the charges, and would have been allowed to make his case for why he should be trusted, etc. In the United States, it is every citizen's right to "face his accuser." In other words, if someone were to level charges against me, I have the right to respond and to try to clear my good name. For example, perhaps the crimes I am charged with were committed by someone who either looks like me or who has a similar name to mine. Or perhaps I was charge with the crimes but the authorities discovered that I was innocent and the charges were dropped or I was acquitted at trial, etc.
In other words, it isn't right to level charges at another person without that person having the opportunity to defend himself/herself. And that is what your emails have done. Again... if everything you said is true and you have incontrovertible proof, then that should be presented.
The other factor involved here is somewhat like the military's "chain of command." If I am a private in the army and I have a problem, then I go first to my sergeant. If he/she cannot resolve the problem, then I would go, in turn, to my lieutenant, the captain, the major, etc., on up the line. It is the same way at work places. If you have a problem with someone, you go first to the worker representative, then to Human Resources, then to the higher officers in the company, and then to the National Labor Relations Board or to a legal process in court or in mediation. You don't just make public charges against another person. At the university, you probably have a "chain of command" as well. Perhaps that would be your R.A. (resident advisor), your guidance counselor, the dean of students, and so forth up the line. If you don't get results from inside the university, you move to the outside authorities and notify them, etc.
Yes, you're in a difficult situation. The fact that your email went to a "Reply to All," or a large list of people, is only an exacerbation of the problem. Even if you have sent it to 10 of your friends instead of a list of 50, it was probably a poor decision on your part.
You need to face up to the problem, explain your intentions, and, if you find in your mind that you were wrong, to apologize to the university, to the students who received the email, and (if you don't have legal proof) to the student about whom you wrote.
Best wishes to you as you navigate these rough waters.