A prima facie case means you have sufficient evidence, that unrebutted, proves a certain fact. This evidence, standing alone would compel a conclusion favorable to the prosecution if the defendant produces no evidence to rebut it. Basically this is enough evidence to get you past a motion to dismiss or motion for a directed verdict.
I don't think he has it because he has to have prima facie evidence as to every fact necessary to prove the elements of his case.
Nifong has an accuser with a rambling story and about as weak a medical report as you can get. The medical report certainly doesn't back up the accuser's story of a three person, three orifice gang rape. It doesn't support the notion that she was hit and kicked. He has no corroboration for her story - either eyewitness corroboration or physical evidence such as DNA. He has a big fat zero.
Unfortunately Mangum's statement unrebutted by the defense is probably is a prima facie case then. While you are correct, the rape exam is about was weak as it can be, it does not show that a rape could not have taken place.
What is going to do Nifong in is his refusal to look at the evidence the defendant's offered him or Roberts throwing him under the bus and admitting he gave her the sweatheart bail deal in exchange for her moving her story toward Mangun's.