Some questions:
What was different in her life now as opposed to 2-3 months earlier? She had lived in town for many of her formative years. She knew lots of people and they knew her. She was a fixture running through town - and nothing had happened. She was in an established long term relationship. She would have (obviously) known her BF's family. She was articulate and intelligent. Is or was there a change in her routine that would have put her in social contact with different people? Like her summer job? Or her summer living arrangements? As far as I know and have been able to read, there is not a history of local crime waves spawned by touring carneys nor the annual detasseling event. Is there someone who would have been introduced to her recently? Any newer SM adds or had she made any new friends? Was she hanging out with anyone new this summer, had someone displayed new or renewed interest socially? Could even be a friend of a friend.
I have a hard time getting my hands around a theory of a local deranged bubba somehow emerging from the corn and being irresistibly drawn to her this summer, when he would likely have seen her over the years.
It is always easy to point a finger at the traveling construction worker. Truth be told, the guys I know are highly skilled and regularly drug tested. While they may trade a lick or two in a bar fight, most of them will not do anything to endanger their jobs, which can pay the skilled trades upwards of $30-$40 an hour plus benefits.