Proving malfeasance after the fact is all well and good. But it doesn't solve the fundamental problem: Even "just" an arrest still results in the loss of your freedom. The fact that you're being held at the police station or jail instead of prison makes no difference. If he did not, in fact, rape those women, and they are trying to frame him for a crime he did not commit; he still faces a loss of freedom, and the actions being taken against him are an abuse of governmental power of the highest and most intolerable order. The problem is, that those sorts of people are tolerated. Have you ever heard of an officer or prosecutor who falsely arrested or charged someone being prosecuted themselves; or even fired as unfit to serve the public?
Why would or should he cooperate, in any way whatsoever, with corrupt government officials who have broken their trust with the public in the worst way possible, and are trying to frame and imprison him for a crime that he didn't commit? Why would anyone? Would you happily take that fall? I wouldn't.
And, on the other hand, he did, in fact, rape a bunch of women; then he is a scumbag of scumbags; and why would it surprise you that he's doing everything he can to get out of it?
Either way, from his perspective, it doesn't make a lick of sense for him to help them out.