That’s what everyone is trying to figure out now. Karr’s name had been brought to Boulder investigators’ attention five years ago, when Sonoma County, Calif., sheriffs alerted them to his conversations with Hutchens, who acted as their confidential informant as they investigated Karr for links to unsolved child murders. (The Sonoma cops had arrested Karr in 2001 for misdemeanor possession of child pornography, but he fled the United States before that case could go to trial.) Last week, Sonoma officials confirmed Hutchens’s role in the case and said they’d warned Boulder investigators about Karr’s “apparent fascination” with the Ramsey case and his “uncertain allusions placing himself in the killer’s role.” Hutchens says she also raised Karr’s name with Boulder authorities. The Boulder D.A.’s office won’t confirm whether investigators received the Karr tips.

Now Karr, 41, sits in a Boulder jail cell, facing possible charges of first-degree murder, kidnapping and sexual assault. After nearly 10 years of frustration in the notorious case, District Attorney Mary Lacy’s decision to have Karr arrested suggests she thinks he may well be the killer. But other signs point to Karr as merely a deeply troubled man who had studied the Ramsey case obsessively. Lacy must quickly decide whether to bring formal charges: under Colorado law, she has only days to file them–or let Karr go.

What finally led to Karr’s arrest in Bangkok began with an e-mail exchange he had in May with a Colorado journalism professor who’d followed the Ramsey case and had corresponded with Karr for four years (Karr never identified himself by name, but instead used a tantalizing e-mail address: the date of JonBenet’s murder). Investigators are now scrambling to match Karr to the case’s evidence, including DNA. Karr’s ex-wife Lara believes he was with her in Alabama when the murder took place; his father and brothers say he was visiting them in Georgia. A Karr family representative, Gary Harris, said last week that Karr “has some serious emotional and psychological problems”–but that he didn’t kill JonBenet. Attorneys for Karr declined to comment.

In 2001, John Karr sent Hutchens an e-mail promising “I have so much more to tell.” Hutchens never got the full story, but with Karr in custody, we may learn just what he did–and didn’t–do.