http://nypost.com/news/nationalnews/73715.htm
I am surprised that police don’t consider him a suspect, or at the very least ask him not to leave town while the investigation is under way.
I’m not sure what criteria is needed in order for someone to be considered a suspect, but I would think that since he was the last person to see her alive, that would surely make him suspect material.
IMHO, it doesn’t necessarily follow that the police don’t know where he is just because his neighbors haven’t seen him in a few weeks. Could be that he’s staying with relatives or friends.
As for his lack of ‘suspect’ status: I reckon the police are suspicious of him, despite the fact that he’s not officially been labeled a suspect. I would think (hope?) that they’re attempting to keep tabs on his location although he’s not legally restricted from traveling.
Or maybe I’m living in Dreamland. 
If he’s guilty, he’s probly out shitt*ing bricks somewhere.
They seek him here, they seek him there, those neighbors seek him everywhere.
Is he on vacation, is he on the run, that damned elusive Peterson?