John Mark Karr, the suspect in the death of 6-year-old JonBenet Ramsey, sipped champagne and ate fried king prawns in business class Sunday after being put aboard a flight to Los Angeles to face charges in the United States.

As Karr wined and dined in style and chatted with the three U.S. officials escorting him, another bombshell emerged: Reports that Karr sought treatment at a Thai sex-change clinic.

His Thai Airways International flight took off about 8 p.m. (6 a.m. PDT) for the 15-hour flight to Los Angeles. Karr's journey will eventually end in Boulder, Colo., where he is expected to face charges of first-degree murder, kidnapping and child sexual assault in connection with the young beauty queen's 1996 killing.

Karr was not handcuffed while being whisked through Don Muang International Airport in Bangkok. At the departure gate, he talked amiably with fellow passengers.

The 41-year-old teacher sat in a business class window seat next to Mark Spray, an investigator with the Boulder County District Attorney's office. A U.S. Embassy official and an agent with "Homeland Security" on his T-shirt were also part of the escort party.

Before takeoff, Karr took a glass of champagne from a flight attendant and clinked glasses with Spray, who sipped orange juice.

Dinner on board, served on a starched white tablecloth with silverware, was one many passengers would envy. Karr started with a pate, then had a green salad with walnut dressing. The main course was fried king prawn with steamed rice and broccoli. Karr drank a beer, crushing the can with his hands when it was empty, then moved on to a glass of French chardonnay with his main course.

"It seems odd to me. If there is an arrest warrant issued, he ought to be under arrest," said former Adams County District Attorney Bob Grant, who was involved in the Ramsey investigation. "It is very strange. Whoever is in control of him ought to make sure he isn't doing things like drinking champagne."

When Karr lands in Los Angeles late Sunday, he will be processed by immigration officials and is expected to be arrested by local authorities on an arrest warrant out of Colorado, said Carolyn French, spokeswoman for the Boulder County district attorney's office.

Karr will then have an extradition hearing in Los Angeles within the next few days, French said. If he agrees to waive extradition, Karr will then be taken to Boulder County.

"If he fights extradition that is a much more lengthy process," French said.

Karr was being brought back to the United States on a temporary passport. French did not have information on who paid for the flight.

The suspect was relaxed, smiling and chatting nonstop with the U.S. officials next to him-until the television news crews on the flight turned their cameras on. Then he stopped smiling, clutched the armrests of his seat and stared at his lap.

Karr did not speak to reporters, but at one point summoned an AP reporter over to his seat. He mentioned an interview she had given, recalling that someone asked her what he was like.

"You said I looked you straight in the eye when I talked to you and I want to tell you I appreciate that, I thought it was nice," Karr told the AP reporter.

Just hours before Karr's departure, a doctor at a seedy but popular clinic in downtown Bangkok 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.

Another employee at the clinic, who spoke on condition of anonymity because she was not authorized to speak to the media, said Karr had talked with the doctor about a sex-change operation. This could not be confirmed by other sources.

Bangkok, where Karr lived on and off for two years, is regarded as a major global 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.

Thep has received considerable publicity for his male-to-female operations and the clinic is one of the sponsors of an annual beauty pageant for transsexuals in the seaside resort of Pattaya.

Karr appears to have been shadowed by gender issues since his early years, according to excerpts of e-mails published in the Rocky Mountain News that Karr wrote to University of Colorado journalism professor Michael Tracey.

Karr said his father was a "strong influence but rarely around," and responded to Tracey's question about whether his "fascination with little girls - which clearly has a strong erotic component-is a way of going back."

"Maybe I am not going back but have simply stayed consistent," Karr responded. "My peer group has not changed since I was a little boy, and girls were the people I was with always. Referring to them as a peer group is somewhat incorrect, but might also be the very definition of what they continue to be in my life."

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.

U.S. officials, the only ones to have actually interrogated Karr, have been silent about what he told them, citing his right to privacy and legal procedures. Secondhand accounts by Thai officials have been vague and contradictory.

Karr told reporters Thursday that he was alone with JonBenet when she died in the basement of her home on Dec. 26, 1996, but that her death was an accident.

However, there is little public evidence linking him to the crime, prompting some experts to speculate that he is either lying or delusional.

"Many high-publicity crimes have these people coming out of the woodwork," said Elizabeth Loftus, director of the Center for Psychology and Law at the University of California-Irvine.

Lawyers for the Ramsey family say a number of people already have confessed to the killing of JonBenet, but none had enough credibility to attract the attention of law enforcement.