The heavy article and news reports say there were people there though... There was a lady that crossed right after they did and a couple as well. So if the killer and the girls were there. She was there too... at the same time and another couple. So that's three people that could have seen or heard them if they were there. :
[A woman who was at the bridge
commented on a Facebook post by a family member of one of the girls, saying she had been at the bridge shortly after the girls posted the photo. She said she didnt notice anything out of the ordinary.
I even walked all the way across the bridge and back. I only (saw) a guy when I first got there and another couple once I got on the bridge, Cheyenne Mekisha Engles wrote. I didnt see the girls at all. I also didnt take the trail that leads to the right. Only took the trail that lead to the bridge.]
http://heavy.com/news/2017/02/liber...ssing-snapchat-facebook-photos-family-bridge/