John Karr, 41, spoke at a news conference Thursday, a day after his arrest for the December 1996 death of the 6-year-old in Boulder, Colo.
"I loved JonBenet and she died accidentally," Karr said.
He will be extradited to Boulder within days, charged with murder, kidnapping and sexual assault on a child, said Ann Hurst, Department of Homeland Security attaché at the U.S. Embassy in Bangkok.
Law enforcement sources told CNN Karr had been under investigation for an unrelated sex crime when information led to his arrest in the Ramsey case.
Mary Lacy, the district attorney in Boulder, told the Rocky Mountain News that her office sent an investigator to Thailand Aug. 7 to make the arrest. She warned that a lot of work still has to be done and said that the case has been and will continue to be a tough one because of the media attention.
"You have to appreciate the difficulty of an international investigation when it's (night in Thailand) when we are working," she said.