How do police prove that someone had sex with a certain person?

Like you see those statutory rape cases n stuff, where both parties deny having sex, and the cops still find the persons guilty? How do they do it?How do police prove that someone had sex with a certain person?its hard to prove if nobody tells unless it just happened then dna comes into playHow do police prove that someone had sex with a certain person?Cops don't find people guilty of anything...judges or juries do, based on evidence.How do police prove that someone had sex with a certain person?Probably lots of eye witnesses.