Welcome What If!
You make good points here. My thoughts:
1) I think, if I remember right, the FBI agent who originally was there helping with the search just happened to be there when the call came in. That doesn’t explain though why they remained on the case but I agree that at least at first LE thought it was a serial type killing. They seem to have pulled off of that with now insisting he’s local. Also, very early, wasn’t there talk of the Dept of Homeland Security being involved in some way? I certainly never understood that...if that’s true.
2) This is a very interesting scenario. I initially thought BG walked them back across the bridge and down the other side. Then LE said at some point that they crossed the creek and I went long with it thinking they meant wading across. How nobody noticed BG with wet clothes afterward has always been a problem. Your scenario does have them crossing the creek, just not wading across. Is LE playing word games with us? Who knows.
Thanks for throwing this out for discussion. Something else to think about!