Karr was arrested at Los Angeles International Airport on a warrant from Boulder County, Colo., after getting off a Thai Airways flight, where he feasted on champagne toasts and roast duck. A helicopter then whisked him to the Twin Towers jail shortly before midnight.
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. An extradition hearing was scheduled for Tuesday morning, the Los Angeles County district attorney's office said. It was not known whether Karr had retained a lawyer.
U.S. officials have not said a word about what Karr told them during interrogations, and Thai officials have backed off of some of confessions they said Karr gave them. U.S. officials also have not yet discussed any charges that Karr may be faced with.
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.
"He is going to be housed here in the men's jail, kept in isolation in a 6-by-9 room with a bed, a toilet no windows and no phones," said Los Angeles County sheriff's spokesman Steve Whitmore. "He'll get jail chow, he won't get king crab, I'll tell you that."
Karr 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.
While in Thailand, Karr had visited a clinic to have facial hair removed permanently because he wanted to prepare for a sex-change operation, a doctor said Monday. Click here to read more on that story
The 41-year-old school teacher's return to the United States was voluntary, and he wasn't handcuffed before or during the 15-hour Thai Airways flight from Bankok.
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.
Before takeoff, Karr took a glass of champagne from a flight attendant and clinked glasses with Spray, who sipped orange juice.
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 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.
Shortly after the Thai Airlines flight landed at LAX, Karr showed his first sign of emotion during the 15-hour flight, according to a FOX News. photographer on the plane. His eyes filled up and he, for the first time, had something other than a blank stare on his face. He didn't actually cry, but he showed emotion.
Earlier this year, Karr had gone to the Siam Swan Cosmetic Clinic and its branches in Bangkok to have his sideburns and hair under his chin removed with lasers, Dr. Setthakarn Attakonpan said Monday.
"He wanted to prepare himself to do a sex-change operation," said Setthakarn, a dermatologist.
Hours before Karr's departure from Bangkok on Sunday, a doctor at a clinic specializing in sex-change surgery said Karr had gone there 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.
The Associated Press contributed to this report.