There are so many red herrings in this case it's unbelievable. Now, I'm not familiar with this case at all, but having skimmed through a few articles and read some points on here, it's clear why this case has still not been solved.
Someone on this thread mentioned first looking at why rather than who, which is very important. This then narrows down the possible perpetrator/s.
There are several pieces of evidence thrown into this case that has made it go wayward.
To me, first impressions lay within organised crime.
The last received text being from someone in Cyprus. The fact that she was planning to go abroad.
Nags head, a local. Was there some sort of drug business going down there? Might explain the man seen lurking around her house, perhaps she owed him money?
She had several secret lovers, some married. Was she an escort?
This all point to an underground mystery.
There are things that have been added to the mix on purpose, to divert attention from what actually happened.
What her friends have said, the people seen arguing, the breakfast dishes in the sink, the bed made, etc. Planted.
Trafficked; she's an attractive woman. In this case, probably killed recently or dropped, she's in her prime now.
Saw something she shouldn't have and threatened to expose; they killed her. (Does this tie in with the time the man was seen near her house?)
She left on her own accord in fear or simply wanted to start anew. (Hair dye)
Organised crime. Rogue officers.
Everyone has secrets.