Nine days after his arrest in Thailand in the death of JonBenet Ramsey, the 41-year-old former schoolteacher now awaits a court appearance that could come as early as next week.
Karr arrived here Thursday, flying in from Los Angeles on a state police plane to face charges in a homicide case prosecutors acknowledged is in its infancy.
A woman who watched as he was brought in last night said he appeared sullen, almost resigned like he had been through this before, reports CBS News correspondent Kelly Cobiella report.
Formal charges were pending and the date of Karr's first court appearance could be announced Friday, the district attorney's office said.
His first few hours at the jail were to include physical and mental evaluations, and he was isolated from the other 480 inmates, Boulder County Sheriff Joe Pelle said.
"Anybody that's in jail in our population that faces these kinds of charges, charges against children, faces some danger," Pelle said.
Questions about Karr's involvement in the case have arisen since he told reporters following his arrest in Thailand that he was with the 6-year-old beauty queen at the time of her 1996 death but that it was an accident.
Boulder County prosecutors have refused to detail any evidence they might have, but in a court filing this week said investigators didn't learn of Karr's name until Aug. 11, five days before his arrest. They said he was arrested in part because they feared he might get tipped off and vanish.
The court filing conflicts with the Sonoma County, California, sheriff, who said his office alerted Boulder authorities about Karr in 2001 after he was arrested on child pornography charges. The sheriff and Boulder prosecutors declined to comment on the apparent discrepancy.
Karr has professed love for JonBenet in e-mails with a Colorado professor, and told a California woman he believes the girl was tortured before she was strangled.
Karr's family contends he was with them in Georgia at the time, while an ex-wife has said she believes he was likely with her in Alabama. Neither she nor the family has offered definitive proof.
Sonoma County sheriff's Lt. Dave Edmonds said Karr expressed an "apparent fascination" with 1993 murder victim Polly Klaas and JonBenet, and "presented ideas about what the murderers of Polly Klaas and JonBenet Ramsey must have thought and felt."
But there was no confession, Edmonds said, or anything else to suggest Karr played a role in JonBenet's slaying.
The Boulder arrest warrant and supporting affidavit remain sealed and the district attorney is fighting media requests to open them. Prosecutors said in the court filing Wednesday the affidavit contains evidence never before disclosed publicly.
Former Denver prosecutor Craig Silverman speculated that investigators may already have DNA evidence that they believe links Karr to JonBenet's death.
He said prosecutors may have obtained and tested DNA from a letter Karr reportedly sent through the mail, and that may have persuaded Boulder County District Attorney Mary Lacy to send an investigator to Thailand to surreptitiously collect more samples.
After JonBenet's father, John Ramsey, found her body in the family's basement on Dec. 26, 1996, police collected DNA from blood spots in her underwear and from under her fingernails.
Investigators have said some of the DNA was too degraded to use as evidence, but some was of sufficient quality to submit to the FBI in 2003. The sample did not match any of the 1.5 million samples in the agency's database, according to the Ramsey family attorney.
Other evidence includes a ransom note, a mysterious boot print found outside the house, marks on JonBenet's body that some say could have been made by a stun gun; and signs that someone may have entered the house through a basement window.
Dozens of attorneys have come forward offering to represent Karr. The county public defenders' office has asked to meet with Karr, the sheriff said. It was not known whether such a meeting had taken place Thursday.