Interesting. I've lived in Cary since the early ninties and have never really seen more than a few "sketchy" people. Usually near Regency Lake when there's an event/concert going on. Cary does have a low crime rate, most of the murders that have occurred here were husbands killing their wives. We've had the guy who tossed his wife off the Cary Parkway overpass, the guy who killed his wife and then sat on the front steps and waited for the police, the guy who killed his wife and then set fire to a vehicle (I think somewhere on I-40).
I can't see Nancy running alone and heading down Holly Springs Road to the neighborhood in which her body was found. If she really went running at the time Brad specified, she would have been on trails in Lochmere, or around Regency, that would have people out doing the same thing. These are not places that "sketchy" people tend to hang out. And no, I don't run, but I do walk in Regency and Lochmere.
I think if Brad was really suicidal he wouldn't be using google to figure out a way to asphyxiate himself. I think it's possible he was looking for a way to make Nancy look like she had committed suicide. If Brad and Nancy were getting along and she disappeared on a run, he would have been begging the police to find her, not hiding in the house on the internet! We also wouldn't have all the CE that makes him the number one suspect.