I have a strange theory about this- it's crossed my mind that the Ramsey's, knowing that the mom was dying and wanted her name cleared, paid Karr to confess and take the fall.
It's obvious to me based on a number of things including my background in non-verbal communication, that Karr is not the murderer. If he did know information that only the murderer would know, he was given that information. I also point out that he has had only sporadic work in over twenty years- how was he able to have fancy cars and live aboard before being arrested. And when arrested, why did he so easily confess?
A lot of questions... I feel very strongly that this man is mentally-ill and that he is not JonBenet's killer.
Just my opinion,