Again, based on decency and morals, it SEEMS very cut and dry to us, but to the police, courts, and lawyers, it's a totally different story. Of the lawyers that I've asked, all of them (admittedly just 4 friends that I asked in passing, and by no means scientific) said, "Eeesh, yeah, that's a tough one, I mean there COULD be a case, but I don't know if I'd take it," for a long list of reasons.
You'd have to get a police officer to take you seriously, and actually file a report. You'd have to find a lawyer to find "merit" and actually take your case. You'd have to find a judge that wouldn't dismiss it as "frivolous". Finally, you'd have to find a jury, that after seeing the "allowable" evidence, hearing the allowed lines of questioning, receiving specific and directed jury instruction, would still find for the victim. It's not impossible, but it would be VERY difficult.
Let me put it this way... Considering how many people are still being infected daily, how often do you hear about one of these cases? Yes, you might be able to come up with one or two anecdotal, or even landmark, cases over the past several YEARS, but if these cases were easy to bring, you'd hear about a few of them on every single installation of the nightly news.