BANGKOK, Thailand -- The district attorney in the JonBenet Ramsey slaying case said Thursday there is "much more work" to be done in the case against the suspect, and she warned the public not to "jump to conclusions."

Mary Lacy, who has spearheaded the investigation for Boulder County, did not immediately disclose any details about the case involving former schoolteacher John Mark Karr, 41, who was arrested a day earlier at an apartment in Bangkok.

But she suggested that the arrest may have been forced by other circumstances, including the need for public safety and fear the suspect might flee.

She refused to answer whether authorities were worried Karr was lying about killing the little girl. Lacy said Karr has not been formally charged, and declined to speculate what counts he might face.

"John Mark Karr is presumed innocent and I can't comment beyond that," she said.

Suspect Claims JonBenet Sexually Assaulted

Karr told investigators he drugged and had sex with the 6-year-old beauty queen before accidentally killing her, a senior Thai police officer said Thursday. An autopsy done a day after her body was found said a blood screening showed no drugs or alcohol in her body but said she had vaginal abrasions.

Lt. Gen. Suwat Tumrongsiskul, head of Thailand's immigration police, said by telephone that he was not present for the questioning conducted by U.S. law enforcement officials.

But, according to what the general said he was told, Karr "said he drugged the child."

Karr claimed he had sex with Ramsey, who was still alive, Suwat said. Karr said he then realized he had "accidentally" killed her, according to the general.

"I am so very sorry for what happened to JonBenet," he told the AP in Bangkok. "Her death was an accident."

Asked if he was innocent of the crime, Karr said: "No."

Karr will be taken within the week to Colorado, where he will face charges of first-degree murder, kidnapping and child sexual assault, Ann Hurst of the Department of Homeland Security told a news conference in Bangkok.

Living In Thailand

In Bangkok, police said Karr had been living in a dormitory-style guesthouse called The Blooms in a neighborhood of massage parlors and travel agents that cater to expatriate residents and sex tourists.

Suwat said U.S. authorities informed Thai police on Aug. 11 that an arrest warrant had been issued for Karr on charges of premeditated murder. The warrant was sent to Thai police on Wednesday.

"Through investigation we were able to determine where his residence was and the Thais arrested him," Hurst said. "He did not resist. He did express surprise."

The U.S. Homeland Security official said Karr had left the United States several years ago and had not returned.

Suwat said Karr arrived in Bangkok on June 6 from Malaysia to look for a teaching job. It was not clear whether he had gotten a job, the police officer said.

Karr's visa has been revoked for being an "undesirable person" after the accusations against him, and U.S. authorities were expected to take him to the United States in the next few days, Suwat said.

Karr lost any legal protection in Thailand after the revocation, leaving Thai authorities free to hand him over to the U.S.

Some Doubt Karr's Claim

No evidence against Karr has been made public beyond his own admission. U.S. and Thai officials did not directly answer a question at the news conference Thursday about whether there was DNA evidence connecting him to the crime.

Karr's ex-wife, Lara Karr, told KGO-TV in California that she was with her former husband in Alabama at the time of JonBenet's killing and she does not believe her former husband was involved in the homicide.

She said her ex-husband spent a lot of time studying the cases of Ramsey and Polly Klaas, who was abducted from her Petaluma, Calif., home and slain in 1993.

As he was escorted to his guesthouse to pick up his belongings, John Mark Karr told the AP: "I am so very sorry for what happened to JonBenet. It's very important for me that everyone knows that I love her very much, that her death was unintentional, that it was an accident."

Asked what happened when JonBenet died, he said: "It would take several hours to describe that. It's a very involved series of events that would involve a lot of time. It's very painful for me to talk about it." Click to listen to the audio interview.

He told the AP he made "several efforts to communicate with Patricia before she passed away," referring to JonBenet's mother, who died in June, "and it is my understanding that she did read my letters."

Karr on Thursday refused to say what his connection was to the Ramsey family. An attorney for the Ramsey family said Wednesday that Karr once lived near the family in Conyers, Ga.

A Cold Case

JonBenet was found beaten and strangled in the basement of the family's home in Boulder, on the morning of Dec. 26, 1996.

Wednesday's arrest was a surprise development in one of America's most lurid murder cases, which had left a cloud of suspicion over her family after years went by with no arrests. Some feared the case would never be solved.

Striking video images of the blonde-haired girl in child beauty pageants helped propel the case into one of the highest-profile mysteries in the United States.

7News reported that Karr had been communicating periodically with a University of Colorado professor in Boulder who had been following the case and cooperating with law enforcement officials.

A University of Colorado spokesman, Barrie Hartman, said journalism professor Michael Tracey communicated with Karr over several months and contacted police. The university spokesman said he didn't know what prompted Tracey to become suspicious of Karr.

Tracey produced a documentary in 2004 called "Who Killed JonBenet?" A woman who answered the phone at a number under his name said he didn't live there anymore; his office phone mailbox was full.

The Ramseys learned that police were investigating Karr at least a month before the June death of JonBenet's mother, Patsy Ramsey, of ovarian cancer, the family said.

In a statement Wednesday, father John Ramsey said that if his wife had lived to see Karr's arrest, she "would no doubt have been as pleased as I am with today's development almost 10 years after our daughter's murder."

Suwat quoted Karr as saying he tried to kidnap JonBenet for a $118,000 ransom but that his plan went awry and he strangled her. Patsy Ramsey reported finding a ransom note in the house demanding $118,000 for her daughter.

Investigators said at one point that JonBenet's parents were under an "umbrella of suspicion" in the slaying, and some news accounts cast suspicion on JonBenet's older brother, Burke. But the Ramseys insisted an intruder killed their daughter, and no one was ever charged.

Evidence In Case?

Boulder authorities wouldn't say what evidence they might have that could connect Karr to the Ramsey murder, however some of the evidence they might be looking at includes:

Forensic evidence from the crime scene that points to Karr.

Any airline tickets or gasoline credit records that put Karr in Boulder at the time of the slaying.

A re-examination of the surveillance tape taken at a local hardware store where police said the distinct cord used to strangle JonBenet was purchased.

Any reservation records from local hotels or motels that might place Karr in Boulder at the time.

Over the years, some experts suggested that investigators had botched the case so thoroughly that it might never be solved. The Ramseys moved back to Atlanta after their daughter's slaying.

"It's been a very long 10 years, and I'm just sorry Patsy isn't here for me to hug her neck," said Lin Wood, the family's longtime attorney.

"John and Patsy lived their lives knowing they were innocent, trying to raise a son despite the furor around them," Wood told MSNBC.

Hurst said Karr has been "very cooperative" with authorities and that he's shown a "variety of emotions."

Hurst, with the department's U.S. Immigration and Customs Enforcement in Bangkok, said that Karr had left the United States several years ago and had not returned.

The immigration and customs office had assisted the Boulder County District Attorney's Office and the Royal Thai Police in the investigation.

The suspect, who has been in Thailand five times over the past two years, was being detained by immigration police pending arrival of U.S. officials, Suwat said.

When asked how he could travel for so many years in Asia, and whether he was independently wealthy, Hurst responded, "We're asking the same questions."

Officials in Boulder said Karr had just started teaching at a school in Bangkok when he was arrested.

Karr Taught In California

Bob Raines, principal at Wilson Elementary School outside Petaluma, Calif., said he twice hired Karr as a substitute in second- and fourth-grade classes in 2001. After observing him, Raines said, he concluded Karr hadn't been trained, had poor skills keeping classes focused and was ineffective.

A couple months later, Sonoma County sheriff's officials sent a letter to school officials saying Karr had been arrested, said Carl Wong, the county school superintendent.

County Chief Deputy District Attorney Joan Risse confirmed the child pornography charges and arrest warrant against a John Mark Karr, though she cautioned that she didn't know if he was the same person held Bangkok. State records show Karr lost his teaching credential in 2002.