I always try to remember confirmation bias when I make a conclusion, although I have still made mistakes. I saw a story about a plane crash, Varig Flight 254, in which confirmation bias played a big role. Basically, the experienced captain got lost, but at the time up in the airplane he had no reason to believe that he was lost. So he followed clues to try to get him back on track which were the wrong clues(because in his mind he thought that he was generally going the right way).
I think that in the case of Abigail Williams and Liberty German confirmation bias is crucial to how the general public as well as the investigators look at the case. Among the general public I am sure there have probably been many sightings of the bridge guy. Some people may think he is young while others believe he is older. The sketch/video interpretation is based in part on that.
As of right now, I tend to think police are under the impression the killer has to be local and from the Delphi area because he knew about the Monon High Bridge trail and how to navigate it. Maybe there is more to it and the police know more than what they say, but I really do think they are basing the killer being local on the idea that the Monon High Bridge is something only locals or someone who has lived in Delphi would know about. And that is it.
Well, we always find out how much info LE has had all along that we never fathomed. They have state police, local sheriffs and FBI all investigating and I'm pretty sure it was the FBI that created a profile of the killer.
I believe the chances of four separate agencies (local police were also involved) and all the personnel in each of those agencies, all operating under confirmation bias that websleuthers are smart enough to recognize (while they aren't) is slim. Add that one of those agencies is the FBI and the chance IMO is zero.