Was he arrested and fingerprinted? if so... his record will mostly show up there... was he charged? what was the sentence?
just be honest to the immigration. It has been 13 years. Unless your friend is still doing, he would be ok. Citizenship requires 5 years of good character. Of course, if you hire a lawyer to go over the case, then it would be better.
he should be ok.
well let me know how that comes up. that would be a good reference here. Thanks.