The probable cause document says that Abby and Libby were dropped off "across from the Mears Farm at approximately 1:49pm." Edit to say: I agree with
@FrostedGlass that this could be closer to "departure time" of KG. Regardless, it wasn't 1:13pm but later.
Based on that same document, it does appear that the juvenile witnesses saw the man shortly after taking a photo of a bench east of the Freedom Bridge, which is the pedestrian bridge across the Hoosier Heartland Highway. At that time, the girls were walking back towards the Freedom Bridge and the man was heading in the opposite direction, towards the Monon High Bridge (same direction as Abby and Libby, but well behind where they would eventually enter on the trail).
If he entered the trail system near the old CPS building, that would be in the general vicinity of the Freedom Bridge area where the juvenile witnesses encountered him. Assuming that is his car parked by the building - if it isn't, then that is, I guess, still up in the air.