The guy is creepy.
I agree he is creepy, delusional, deranged, maybe.
But he didn't kill JonBenet.
He is a handy scapegoat, brought to the DA's attention by Professor Michael Tracey, who is a friend of the Ramseys and is currently writing a book about the case. Tracey engeged Karr in an online correspondence of several months duration, and it sounds like a sting to me.
Tracey has accused many, many other individuals of killing JonBenet in his poorly-produced documentaries made for British TV.