One of the things I've had to get my head around in posting about this case is the concept of "falsifiability".
https://en.wikipedia.org/wiki/Falsifiability?wprov=sfla1
The scenerio PIP have presented over the years is inherently falsifiable, and when no one actually can falsify it, that's what points to innocence for the pair.
In any of the many PGP theories, particularly the ever shifting motives offered, spend copious amounts of time removing the items which falsify each of the PGP scenerios.
Case in point: I've never once heard a PGP theory even address that Amanda's DNA was collected from the very bathroom she'd used for weeks.
Instead of admitting that that should be incorporated as (at least in theory) something which might falsify their views - they simply ignore it. Never mention it. Deprecate it as a "PIP talking point", and hope the deprecation itself distracts.
The flaky eyewitness testimony is the same. Simply ignore the problems with it, or default to, "It's a judicial truth, and that settles it."