This answer assumes the person in question has been convicted of those crimes. If he has not, things will be easier (but not a cakewalk).
The conviction and expulsion will affect him quite significantly, given that some universities require applicants to declare both certain criminal convictions (usually sex, violence, or drug convictions) and any previous expulsions. Trying to hide convictions is a very bad idea.
Sure, you can find a university who does not require a declaration (or will admit the applicant anyway, if the university is sufficiently satisfied that the student has reformed) - the likelihood of such probably varies by country. I suspect life as a graduate student would be very difficult (getting teaching positions may be hard).
This question reminds me of an article I read a while ago. This man was a convicted murderer, and has turned his life around and obtained a PhD in psychology.
Any specific advice would be subject to the laws of his country, the policies of the universities, and more specific details of the conviction (read: off-topic for StackExchange).
There will always be roadblocks, especially with sex and abuse convictions. Repentance and perseverance may clear enough to find a path through, but it wouldn't be easy.