Just a week and a half after Karr's arrest in Thailand was seen as a remarkable break in the sensational, decade-old case, prosecutors suggested in court papers that he was just a man with a twisted fascination with JonBenet who confessed to a crime he didn't commit.
"The people would not be able to establish that Mr. Karr committed this crime despite his repeated insistence that he did," District Attorney Mary Lacy said in court papers.
CBS News Denver affiliate KCNC's Rick Sallinger reports that hair and saliva taken from Karr in Boulder after his arrival last week were tested over the weekend at the Denver police crime lab and that he was ruled out as the source of the DNA taken from the crime scene.
The 41-year-old schoolteacher will be kept in jail in Boulder until he can be sent to Sonoma County, Calif., to face child pornography charges dating to 2001. An extradition hearing was scheduled for Tuesday.
The district attorney vowed to keep pursuing leads in JonBenet's death: "This case is not closed."
Karr was never formally charged in the slaying. In court papers, Lacy defended the decision to arrest him and bring him back to the United States for further investigation, saying he might have otherwise fled and may have been targeting children in Thailand as well.
CBS News legal analyst Andrew Cohen says because officials were worried Karr would bail if they tried to get DNA tests in Thailand, they figured they'd better get him back to the U.S. and do the tests.
"The problem with doing that is you don't have a strong physical case and it's a red hot media blitz and everybody creates these large expectations for what this guy is or isn't," Cohen says. "It's a huge embarrassment for Boulder."
Lacy said Karr emerged as a suspect in April after he spent several years exchanging e-mails and later telephone calls with a University of Colorado journalism professor who had produced documentaries on the Ramsey case.
According to court papers, Karr told the professor he accidentally killed JonBenet during sex and that he tasted her blood after he injured her vaginally. But the Denver crime lab conducted DNA tests last Friday on a cheek swab taken from Karr and were unable to connect him to the crime.
"This information is critical because ... if Mr. Karr's account of his sexual involvement with the victim were accurate, it would have been highly likely that his saliva would have been mixed with the blood in the underwear," Lacy said in court papers.
She also said authorities found no evidence Karr was in Boulder at the time of the slaying. She said Karr's family provided "strong circumstantial support" for their belief that he was with them in Georgia, celebrating the Christmas holidays. JonBenet was found beaten and strangled at her Boulder home on Dec. 26, 1996.
Defense attorney Seth Temin expressed outrage that Karr was even arrested.
"We're deeply distressed by the fact that they took this man and dragged him here from Bangkok, Thailand, with no forensic evidence confirming the allegations against him and no independent factors leading to a presumption he did anything wrong," Temin said.
In an interview Monday with MSNBC, Gary Harris, who had been spokesman for the Karr family, said he knew the DNA would not match.
Karr has been "obsessed with this case for a long time. He may have some personality problems, but he's not a killer," Harris said. "He obsesses. He wanted to be a rock star one time. ... He's a dreamer. He's the kind of guy who wants to be famous."