Oh, I could see him being the perp in a number of possible outstanding sex crimes with little girls but NOT the one they are hoping to solve. There's just too many very loose ends to make this an open-and-shut case.
I did read the high school entry that Karr supposedly wrote and he does use the same "hooked" a that stood out in the ransom note but not consistently. I have a hard time believing the handwriting is a match but it could with a few more samples to compare against.
FYI