Looks like this was a long stretch of road, no street lights, very cold night. The perp could probably see if another car was coming along for some distance.
In the photo I posted, I thought it looked like the photographer in the depression near the tree. I suspect that there was evidence there. The "not intact" part could have happened at the location ... in which case she was most likely alive until that time. That also leaves the possibility that she was adducted and assaulted in a vehicle - similar to the case with the Cody, WY victim. Friday night, after dark, she was probably taken to that location. The perp probably cleaned everything up during the might, slept during the day, and left the backpack in a different neighborhood just before he hit the road.