It depends on the circumstances...if the victim (assuming victim was a she, although both men and women can be victims) says she was raped by a man--i.e., by someone with a penis--and had semen for evidence, and says, "Pinki did it!"...but Pinki tells the police, "I couldn't have--I'm a woman, don't have a penis nor do I have semen", the police must confirm or deny one of the versions.
The victim's word is enough to start with, but Pinki's assertion can be medically verified (or denied) using a standard medical examination (in the US, that would have to be court-ordered).
The real story (and one that hurts us) is that Pinki was presenting as a woman, yet was able to rape.