The question is: why?
Somebody is being protected. Somebody with power, apparently. It's not Crystal.
Well, the local TV stations are using her name; and they have finally investigated and she is NOT a registered student at NCSU.
As you stated, the "police Chief that didn't bark."
She may well be an informant who meets regularly with some cop who is her handler. It may be a condition to avoid prosecution on some other matter.
The untested DNA may belong to some LEO.