It used to be that to prove rape, you had to show "force" which meant not just lack of consent but convincing evidence that the rapist used violence.
Again thanks to the liberals feeling sorry for the guilty, "force" was reduced to "lack of consent", which means that all the cases of morning-after remorse began turning into rape accusations. Not that you didn't have some anyway, e.g. the Scottsboro trial, but that was not a problem of proof (there wasn't any) but extreme racial prejudice on the part of the community. Even so, Judge Horton stood against popular opinion and set aside the verdict (he lost his seat as a result, but what profiteth a man if he gain the whole world but lose his soul?)
But if rape were actually made a capital offense again, you would see the evidentiary standard change back to its original position. It would have to, because of the strictures surrounding the DP.
I'm not as concerned about the "eliminating witnesses" argument, as they do that now in convenience store robberies. An evil person who would violently rape is likely going to eliminate witnesses anyway.
I don’t think a high percentage of rapes end in murder. Correct me if I am wrong.