I think it's far more likely the girls had plans to meet with someone or told someone (maybe inadvertently) they were planning to go or where they were rather than running into some random murderer in Delphi on a nature trail on a Monday afternoon.
The girls wouldn't have had a car parked out there, so no one would have even known they were back there unless by chance someone was walking/living/driving close enough to maybe hear them laugh or scream or talking. There are a couple of houses on both sides of the creek that would have been very close to where they were dropped off and found. There could have been other trail walkers there as well, but I would imagine an older teen/adult trail walker would have parked and walked in. Wonder if anyone driving by between 2 and 4-ish noticed a vehicle parked either at the parking spot at the trail entrance or along the road on the north side of the creek past the entrance?
If the Snapchat time of 2:07 is pretty concrete and they were to be picked up between 3 and 4, someone had less than an hour to less than two hours to find and kill two teenage girls, possibly move them away from the trail before or after, and get out of there. Because it sounds like whoever went to pick them up started looking and yelling for them immediately.
