BOULDER, Colorado (CNN) -- Far from laying to rest the 10-year mystery of who killed JonBenet Ramsey, the stunning admission Thursday by John Mark Karr in Bangkok, Thailand, only deepened speculation about whether the soft-spoken schoolteacher committed the crime.
Citing ethical rules and the ongoing investigation, Boulder District Attorney Mary Lacy declined to discuss what evidence, other than Karr's post-arrest admissions, linked him to the 6-year-old beauty queen or the Ramsey family.
"John Karr is presumed innocent," she said, adding that investigators had "much more work" to do and urging people not to rush to judgment. (Watch authorities caution the public against convicting Karr -- 4:30)
Lacy also seemed to suggest the investigation is continuing.
"There are circumstances that exist in any case that mandate an arrest before an investigation is complete," Lacy said, citing public safety and the possibility of flight as two such reasons.
She insisted that her comments were generic, however, and that she was not commenting directly about the Karr investigation.
The 41-year-old American was being held at a Bangkok immigration detention center. He faces charges in the United States of first-degree murder, kidnapping and sexual assault on a child, said Ann Hurst, a Department of Homeland Security attache in Bangkok.
In comments before reporters in Bangkok on Thursday, Karr admitted to being involved in Ramsey's death.
"I loved JonBenet, and she died accidentally," he said. Asked if he was an innocent man, Karr replied, "No." (Watch Karr's admission -- 1:15)
Karr also had told an American investigator he had drugged Ramsey and sexually assaulted her before accidentally killing her, said a Thai police official, Gen. Suwat Thamrongsrisakul. (Watch a criminologist explain why people confess -- 2:13)
Karr asked police what charges he was facing, Thamrongsrisakul said. When police replied first-degree murder, Karr said: "No, it's second-degree -- it wasn't intentional," according to Thamrongsrisakul. (Watch authorities describe what Karr told them -- 14:54)
Ramsey's body was found in the basement of her family's Colorado home during the Christmas holiday in 1996. Autopsy results showed she received a massive blow to the head and was strangled with a rope that the killer tightened by twisting an attached paintbrush handle. An autopsy did not detect any drugs in her system.
U.S. and Thai officials are working on clearing Karr's return to the United States, although no date for the extradition has been set.
U.S. Immigration and Customs Enforcement agents and Thai authorities worked closely on the case for two months prior to his arrest on Wednesday, Hurst said.
At the time of his arrest, Karr was under investigation for an unrelated sex crime, two law enforcement sources told CNN. Officials in Bangkok said he had traveled to Thailand -- a country notorious for its child sex trade -- five times in the past two years.
Karr on Tuesday started a new job as a second-grade teacher at a school in Bangkok.
Brother, ex-wife refute Ramsey connection
Karr's brother, Nate, told Atlanta Fox affiliate WAGA that his family will provide information Friday to prove the allegation that Karr killed Ramsey is "just ridiculous."
Karr's ex-wife, Lara Karr, said she also doubted his admission that he had killed Ramsey, saying the couple were together in Alabama that entire Christmas season.
Lara Karr filed for a protective order in October 2001 to keep him away from her and their three sons, citing his child pornography arrest that April. In court documents she said that in 1996 -- months before Ramsey was killed -- an Alabama school district had dropped Karr as a substitute teacher because of concerns he was "too affectionate" with children.
Bravell Johnson -- the school superintendent in Marion County, Alabama -- confirmed Karr's employment as an elementary school teacher in August and September 1996 and that parents' complaints led to Karr's dismissal.
Karr fascinated by Ramsey case
Karr researched the Ramsey case extensively and was riveted by it and the 1993 slaying of 12-year-old Polly Klaas in Petaluma, California, where he and his wife lived in 2000, Lara Karr said.
Police in Sonoma County, California, said Karr was charged with five misdemeanor counts of possessing child pornography in 2001 but failed to appear in court after bailing out of jail. Karr had been working as a teacher and substitute teacher in Petaluma and Napa.
Lara Karr said in the divorce petition that she was 16 when they married and initially did not know about his Internet activities or his propensity for "kiddie porn."
Karr's arrest in Bangkok was the culmination of a probe that began after University of Colorado professor Michael Tracey contacted authorities in Boulder. (Read how the suspect corresponded with the professor)
Tracey, who produced a documentary about JonBenet's killing, had been in touch with Karr for at least two years, according to university spokesman Barrie Hartman.
Karr's e-mails to Tracey were initially innocuous. But when they became "weird" the professor contacted authorities with information that included a code name for the source of the e-mails, a law enforcement official said.
With the help of agents from Immigration and Customs Enforcement, the e-mails were tracked to Thailand.
The break came less than two months after JonBenet's mother, Patsy Ramsey, died of ovarian cancer at age 49. The arrest likely will dispel the cloud of suspicion that has hung over her parents for nearly a decade.(Watch Jon Ramsey react to the arrest -- 2:17)
Karr told The Associated Press he wrote Patsy Ramsey before her death to express his remorse.
"I conveyed to her many things, among them that I am so very sorry for what happened to JonBenet," he told AP, which described him as sweating and stuttering. (Read the full interview)
Karr said he made several attempts to contact Patsy Ramsey, adding he believes "she did read my letters and she was aware of me before she passed away."