I just don't see why two young girls would leave home, walk 15 minutes to a bridge, then turn right around and head home. That is assuming that they have evidence that the girls reached the bridge. I would think they would hang around there, not just turn around and head right back. But according to that map, they were shot between Taylor's home and the bridge. And there's a very narrow time frame for all this to happen in.
If they went to the bridge, then they travelled 1.25 miles in less than 30 minutes:
3/4 mile to the bridge
1/2 mile back to where they were found
That doesn't allow for any time for goofing off at the bridge, which makes me think they saw something there. Not necessarily drugs, but it had to be something criminal enough that the perpetrator had to kill them to prevent them from telling.
(and then there's one more scenario too creepy to even think let alone type)