Los Angeles police detained Karr on a warrant from Boulder County, Colorado, after he arrived in California from Bangkok, Thailand, and turned him over to the county Sheriff's Department late Sunday, said sheriff's spokesman Steve Whitmore.
CBS Radio News correspondent Steve Futterman reports that a media circus developed at the airport, with reporters from both inside and outside the United States gathering. Outside the international terminal more than a dozen satellite trucks were waiting for Karr's arrival.
A helicopter brought him from the airport to the sheriff's Twin Towers jail shortly before midnight in a sobering end to a day that began in Bangkok and included champagne and fine dining aboard a Thai Airways flight.
"He is going to be housed here in the men's jail, kept in isolation in a 6-by-9-foot room with a bed, a toilet no windows and no phones," Whitmore said. "He'll get regular food. He'll get jail chow, he won't get king crab, I'll tell you that."
Karr was to be held in a "high power" cell for noteworthy inmates, checked by guards every 15 minutes, and separated from other inmates who often target suspected child molesters, sheriff's officials said.
Boulder County authorities said Karr was expected to have an extradition hearing in Los Angeles within days, and would be taken to Colorado if he waived extradition. No hearing date was immediately set.
Karr, who last week suddenly emerged as a suspect in a case long believed to have gone cold, told reporters in Thailand that he was with 6-year-old JonBenet when she died in the basement of her home on Dec. 26, 1996, but that her death was an accident.
U.S. officials have been silent about what Karr told them during interrogations.
The 41-year-old school teacher's return to the United States was voluntary, and he was not handcuffed before or during the 15-hour flight.
Dressed in a red, short-sleeve, button-down shirt and black tie, Karr was whisked through Don Muang International Airport in Bangkok. He chatted with fellow passengers at the departure gate.
Aboard the jet he took a window seat next to Mark Spray, an investigator with the Boulder County district attorney's office. The escort also included a U.S. Embassy official and an agent with "Homeland Security" on his shirt.
Karr first dined on pate, salad, fried king prawn, steamed rice, broccoli and chocolate cake. He also had a beer—crushing the empty can with his hands—and then had a glass of French chardonnay.
Karr appeared to order the drinks himself.
He later dined on roast duck with soy sauce and yellow noodles, and for his third meal had pizza, chocolates and a bottle of Evian.
He sometimes conversed with Spray, who took notes on some of the remarks. Karr told an AP reporter that it was "small talk."
Also during the flight, Karr flipped through movie channels, watched "The Last Samurai," dozed and made several trips to the restroom accompanied by two guards. Each time the door was left slightly ajar.
At one point he changed out of the red shirt and tie, replacing them with a blue polo, but then changed back into the shirt and tie before the landing.
Hours before Karr's departure, a doctor at a Bangkok clinic specializing in sex-change surgery said Karr had come in for treatment.
"He was one of my patients," Dr. Thep Vechavisit of the Pratunam Polyclinic said. He refused to provide further details.
Bangkok, where Karr lived on and off for two years, is regarded as a center for sex change operations. The Pratunam clinic advertises sex-change surgery for $1,625—a bargain compared to U.S. prices, where male-to-female reassignment surgery can cost tens of thousands of dollars.
Karr, once detained on charges of possessing child pornography, in recent years apparently traveled to Europe, Central America and Asia to search for teaching jobs. He taught in at least two Thai schools.