There are only 2 theories that make sense to me in my mind.
The first is one Ive posted before. Lindsay wanted to spend the night somewhere, anywhere, since she got turned down at KKs. So she decides to go to a different friends house to ask if she could spend the night, if the friend can spend the night at HER house, or maybe even just to hang out before her 10pm curfew. So she knocks on the door, and a relative (older brother, father, uncle, etc) of the friend answers. He/she is home alone. The rest of the family is out of town, or will be gone for a few hours. The relative is home alone, so he tells Lindsay that the friend will be back in a few minutes, and to come on inside. Or, he tells Lindsay that he is just on his way to pick up the friend from wherever she is at, and would Lindsay like to come along? Then he drives off to do what he intends, since this will give him even more time away from his house and from worrying that the rest of the family will be coming home. This could explain why her scent was not found on the route she should have taken if she had gone straight home from KK, and why she was not captured on surveillance. Also, why theyve searched all over McCleary and havent found a trace of her. The perp may have driven an hour away to avoid suspicion.
The second is scarier because it could happen to anyone at anytime. A SO (not necessarily a registered one) is visiting a friend or neighbor in McCleary. About 9pm, he decides its time to start heading home. As hes leaving, or while hes at Shell pumping gas, he notices Lindsay walking alone. If hes a frequent visitor to the town, hes noticed her before, or even talked to her. Especially if hes fairly young, attractive and charming. Also, because I dont think Lindsay would willingly get in a car with an old, ugly man she didnt know. But if shes seen or talked to someone like I described, she might not see the danger in him giving her a ride the rest of the way home or whatever lie he told her to get her to go in the car. I dont think she was forced into a car, someone would have heard something. Again, this may also explain the lack of a scent and no one hearing a scream.
What do you guys think? Now the hard part is figuring out who the perp is! But to me, these are the only things that would explain lack of a scent, no one hearing anything suspicious, etc.