First of all, I'm so so sorry that happened and that he clearly hasn't felt the consequences of his actions, it's pretty horrifying to me that a rapist can gain acceptance into medical school and this situation can arise.

I would advise that you speak to your premed adviser as soon as possible about this, if you trust them enough to share this with them. If not, one of the adcoms on SDN I'm sure would be happy to help you, and I'd recommend posting this there because they will be able to give you more professional advice. While I do think it could be a good idea to report him, and get at least something on his file about an allegation of sexual assault, at this point you'd probably need to file a legal case (not legal advice, I'm not an attorney) in order to get his acceptance pulled, and there's plenty of reasons why you might want to do that, and also some reasons why you might not. That's attorney territory, but my guess is he would have due process rights now that he's been accepted, whereas it would have been much easier to have his file blackballed before the acceptance was granted.

In terms of a deferment, I think that's an intelligent option to pursue, and it's something again that you can get better advice about from someone more closely involved with the process like your adviser or an adcom. I would imagine they'd grant one for this circumstance, and then it's up to you whether you're alright with going to medical school with him if he's not in your class, again a personal decision that you may want to seek professional help about. This is a terrible thing to happen especially in at your top choice, and I just hope you're able to find a good solution, closure, and ideally can prevent a dangerous man from entering medicine.