My instinct on this is that the DA was duped by so-called 'privileged' information in emails to the CU prof. What she didn't realize was that all that info was already out - and Karr was obsessed with researching the case. Any snippet of info that has come out about the case he was wise to the minute it got out.
The only way they could nab this guy would be with DNA or some kind of inconvertible special knowledge he has. I don't think they've got either.
He was/still is obsessed with Jonbenet, but got his info about her and her death, the same way he got the info about Polly. And he didn't start talking about Jonbenet until she'd been long dead. Yes, the man is a pervert, yes he IS into kiddie porn, and yes, he IS creepy, but there's NOTHING whatsoever to link him to Jonbenet's murder and a whole LOT of things to NOT link him with it.