The thing I keep thinking about with this road is that if one wants to continue south and head away from the village and the campground, they have to go pretty far to reach any kind of regular road or autobahn. Quite far. Far enough that if the family were discovered quickly, a car speeding down a narrow road like that would be noticeable and they would have to go pretty far.
The other thing is the time. I can see the family going out for a walk or something but at that hour and at that road? I just can't see that was the purpose. I think someone followed them and waited, could have even been two cars telling each other where they were traveling.
It was mentioned early on that he kept putting air in the back tire at the campground. If he tried to gun it and the tire was a little flat, it could explain also the indent in the dirt.
It was also mentioned that the guy who found them broke a window to shut the car off. I'm not sure I would bother with shutting the car off if I found a scene like that - I'd want to hightail it out of there as fast as I could without going in my pants. But now that I think about it, if the car WAS an automatic and it was in reverse, it could explain why he wanted to get it to stop. Not sure if that's how it would be with an automatic though, never owned one and can't really drive one so good so not sure.
If all the doors were in fact closed, how did the girl get out of the car and what, she bothered to shut her door? I can't see that either. And if a door was open with the car running, I would think the killer would shut it off as to not draw attention further.
My theory is that the father was selling some kind of secret and the 'buyer' simply wasn't going to pay up. It could also explain the way the father kept leaving the campsite, maybe he was telling the person "not here, let's go here" etc. He may have wanted to be as far away as possible from where others could see anything.
I don't know, rampling thoughts are all I have. This is something out of a crazy spy movie. I think we will learn a lot from this little girl but my god I hope these girls change their names and move to some remote place because someone didn't want them to live.