Here's the thing. ND claims they had investigators for this now.
Manti had supposedly talked to her by phone every night. Which means, if he's telling the truth, there is a real phone number attached to that. And that number will have a real account holder attached to it. Which means the investigators should know exactly to whom Manti was conversing with.
But ND didn't seem to mention anything about knowing who it was. They just said the're keeping everything "private" for now. They could have said "we know now exactly who the girl he was talking with over the phone was but we can't reveal it for legal reasons right now." Nope, instead the guy said something completely different.
Manti has to explain the girl on the other line and who it was really soon otherwise no one is going to begin to buy his side of the story.
ND's investigators, if they ever actually existed, are ultimately working for the university - it was in the university's best interest to cover it up.