Have you talked to your parents? I suggest doing that first, they may have some good feedback on what to do next.
Next thing: You say he 'accidentally' showed nude pictures at school. Is administration aware of this? Are you happy with the response?
With the 'jewish girls' remark, where did you hear this from? Firsthand? From someone else? If it's someone else, does it sound like it has any truth to it? Is it someone you trust who told you, or does it sound like a rumor? If it was firsthand, who else knows about it?
Has he had any complaints filed with administration before? Are you aware of any other incidents?
And, lastly, but probably most important. Sorry to be a little bit awkward here, but the situation in itself is awkward. Have you seen him 'looking' at people? If so, are you sure? Could it have possibly been just a coincidence?
I'd say continue to watch him, but don't draw attention to yourself. By all means talk to your parents. Observe him with an open mind, it won't work well if you approach it with a biased mindset that he is guilty.
I hope you can work this out.