Let's talk profile. I have read in a few places where there is speculation of a truck driver, con, person who travels in an RV, etc. I am on a little bit of a different track based on what I see in the pictures, so I thought I would share.
The man in the photos seems to be very well dressed and well groomed. He has hunting related attire on, but it appears off the shelf (new or does not seem to have been used many times). His hat is camo and he also has a tactical gear or concealed weapons fanny pack that his right hand is in in the first frame and then seems to be out with a possible black handgun now exposed in the second (the one where Abigail William's coat is visible). It also could be the lighting or an odd wrinkle in his clothing, but I wonder if he is wearing a knee guard (as used in hunting or laying floors) because his left leg has an odd shape that would possibly match that product.
Studying these photos, my belief is that this man was watching the bridge for the purpose of "hunting" a female human. This is why - I believe portions of his attire were bought for this day or in planning for this day. He has money and may not be someone anyone else would even think could possibly be involved. Possibly law enforcement or someone in a field that requires you to be well groomed, possibly someone who just has plenty of money to spare. He has been to this area before and knows that that bridge/ trail would be extremely difficult to escape from. I can not tell if the girls encountered him on the bridge or on the trail, but if it were on the bridge and he had a gun, there would be virtually no way they could escape during the initial encounter besides jumping. I believe when he saw his targets he approached and I believe that he had possibly been waiting for a while for the right victims to come along, much like hunting an animal.
I am not convinced he is a current resident, but possibly someone who grew up there and moved or possibly has family in the area. I think he knew the area and understood that that would be a place where a person would be vulnerable. I believe if it were a resident he would have already be in custody, but if it were someone very unsuspecting it is possible he is there.
I earned my degree in criminal justice and this case has caught my attention. Whoever did this is extremely calculated and went to great lengths to commit this crime, in my opinion. I think the person it will end up being may shock some.
While I agree wholeheartedly with most of your post (who am I to agree or disagree....I'm just a run of the mill doofus) I myself am being very careful not to read much into the picture as far as hats or weapons etc and then using said analysis to extrapolate further information such as: he has a camo hat so he has on hunting attire....its not iron-clad he has a hat on...
That said, I fully agree with you on the notion that he absolutely meticulously planned his day and the eventual outcome. I'll speculate further that he not only trapped them on the bridge exactly as you described but that he also lured them there in the first place.