[user104658]

It's extremely complicated as it's only beneficial (including for the victim) for the police to proceed if there's a decent chance of securing charges... and the nature of sexual assault means that "beyond reasonable doubt" is very difficult to prove without evidence of force (when threats, intimidation and coercion are used as often if not more than force) and there are often no 3rd party witnesses.

It can actually be psychologically worse for the victim to proceed only for the casxe to be dropped or lost because of lack of evidence. Mainly because people are dumb about legal things - if it goes nowhere in the first place a lot of people are willing to say "Maybe, who knows". If it's pursued and then dropped, people start saying "Oh he was found INNOCENT so she was LYING!" when in fact there was just no hard evidence.

I don't know what the answer is.