Forensics. Keep gathering samples and testing. IMO
I would retrace it from the beginning, doubting every position of own theory.
They asked to be driven to the bridge. It happened several times during the week, BP says. Someone saw BG there for several days. Did they agree to meet, and was he waiting for them, for several days? Why the bridge?
Abby was never on the bridge before, is it true? Could it be so that the photograph of her on the bridge was taken on another day and merely posted on that day? )Unlikely, since Libby was using BP’s phone, but still).
Was it an attack, or did he lure them down the hill ?
The whole timeframe of murders. Is there a scenario according to which they were alive in the evening of 2/13? Where could they be kept?
LE went with a non-local and a different photo. Why? Who persuaded them?
Who persuaded them to abandon a non-local theory? Could “the local” theory still be wrong? The local narrows the circle. What non-local could know enough about the bridge, and the girls? What would tie a nonlocal to the Monon bridge?
Check everyone who was initially less than cooperative. Why?
Who told LE that the girls had the history of running away? Did they call CPS, or was it the girls’ friend, relative, or friend’s person?
Etc, etc. they can’t get much information two years later, they have to sieve through the facts of that day.
I’d show the photo to the neurologists at Mayo Clinic, they always post stuff about the gait. Ask them if they see something off. And maybe, to local neurologists - did they see someone consulting them who’d walk like this?