I doubt that anyone thought it would take this long at the beginning of the investigation. I think detectives need to start doing some guessing because waiting for factual evidence to find this person and link them to the murders of Abigail Williams and Liberty German may take some time.
There is some information that you can take away from the past 2 and a half years. First, no one has been able to identify the bridge guy suspect. Second, no one seems to know where he parked his vehicle.
I am going to make my complete guess that if you consider this case could be linked to the Evansdale, Iowa murder case, then it would seem the killer is moving east. So maybe this killer is smart enough not to kill in the same area where he lives? And the fact that no one has been able to identify the killer's vehicle is also interesting. Maybe the killer is smart enough to realize that license plates give people an idea of where you are from?
So my complete guess would be that this killer is probably transient and lives in a state west of Evansdale, Iowa. I know that leaves a lot of possibilities. So in order to solve this case, it could take a while.