OK, now that we know the car was parked there on the 13th and not the 14th, I vaguely remember a statement regarding someone seen walking along the Hoosier Hwy. I heard it once and no more after that point. If that is true was it the killer?
Regarding whether LE was indicating whether it was the car or building that is abandoned here is a news article that indicates the vehicle might have been seen at 6814 W. 300 N and there appear to be a couple of buildings in that general area. If that is correct it is not that far to walk to the trail. A car seen at an abandoned building would cause it to be noticed.
Police: Delphi killer 'hiding in plain sight' as new images released
If this killer left his car there instead of the regular parking for trail users, did he do that because the lot was full? OR did he not want his car seen in the lot that day and thus connecting him to the trail? That second point would seem to indicate this was a premeditated act. He either specifically went after Liberty and Abigail OR he was deliberately hunting for a target of opportunity.