Karr, who told reporters Thursday that he was "with JonBenet when she died" but that "her death was an accident," began teaching children in Georgia and Alabama before he became a substitute in Petaluma, a bucolic wine country town where he lived until 2001 with his wife and three sons.
The Denver Post reported that Karr, 41, disappeared that year after being released from jail, where he had been held on child pornography charges. His father, Wexford Karr of Atlanta, told the newspaper his son had told him he was behind bars in connection with the Ramsey case.
Timeline: The JonBenet Ramsey Murder Investigation
Sonoma County Chief Deputy District Attorney Joan Risse confirmed the pornography charges and an outstanding arrest warrant against a John M. Karr, though she said she didn't know if he was the same person held in JonBenet's 1996 death in the child's Colorado home.
Lara Karr of Petaluma, who divorced Karr in 2001, told KGO-TV in San Francisco that he often spent time reading up on the cases of Ramsey and Petaluma resident Polly Klaas, who was abducted and slain in 1993.
His father told The Denver Post that while Karr was in college as an adult, a professor encouraged him to write a book about the Ramsey case after being impressed with a school paper.
"He researched everything he could about her," Wexford Karr said.
John Karr spoke with JonBenet's grandparents, but the Ramseys refused an interview, Wexford Karr said.
He said he feared his son may have been dead before hearing about the arrest Wednesday in Thailand because he hadn't heard from him in several years.
John Karr declined Thursday to say what his connection was to the Ramsey family.
An attorney for the Ramseys said Karr once lived near the family in Conyers, Ga., but the Ramseys moved to Colorado when JonBenet was a baby. The head of Thailand's immigration police, Lt. Gen. Suwat Tumrongsiskul, quoted Karr as saying that he tried to kidnap JonBenet for $118,000 ransom but that the plan went awry and he strangled her. "He said he was in love with the child, she was a pageant queen," Suwat said.
Two resumes posted online with Karr's name and picture offered possible clues to his whereabouts after he left California.
Starting in 2001, one resume said, Karr was a private teacher and caregiver in Germany, the Netherlands, South Korea, Costa Rica and Honduras, almost always working with young children. The other resume was less detailed.
The longer resume said that in Germany he cared for two girls, ages 5 and 8, and a boy, 10, getting them ready for school and helping with homework.
"At days end, I made sure the children had their evening bath, then put them to bed and read to them before they went to sleep," the resume said.
From 2004-05, the resume said, he worked as a second-grade teacher in Honduras.
The authenticy of the resumes could not be confirmed. An English institute removed the shorter resume from its Web site Thursday in response to a reporter's query, citing concerns about bad publicity. A call to the administrator of the site with the longer resume was not immediately returned Thursday.
Karr, a short, thin blond with a Southern accent, had a valid California teaching credential and passed the background check that included submitting his fingerprints to the Department of Justice to make sure he had no criminal record, Sonoma County school officials said.
But his desire to teach didn't translate into ability, according to one administrator.
Bob Raines, superintendent and principal at Wilson Elementary School outside Petaluma, 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.
"He just seemed like somebody who thought he wanted to be a teacher," Raines said. "After a few days, I could see it just wasn't for him."
He instructed his secretary not to call Karr again unless they were desperate.
A couple months later, Sonoma sheriff's officials sent a letter to school officials saying Karr had been arrested, said Carl Wong, the Sonoma County superintendent of schools.
John and Lara Karr's former Petaluma neighbor, Sylvia Ross, said she occasionally asked him over to her house to fix her computer.
"Personality-wise, I think there was a little kink that I saw," said Ross, a retired schoolteacher and real estate agent. He was "too friendly, too talkative, too inquisitive."
Karr's interest in the case apparently continued during his foreign travels.
A law enforcement source, speaking on condition of anonymity, told the AP that Karr had been communicating periodically with somebody in Boulder who was cooperating with law enforcement officials.
A spokesman for the University of Colorado, Barrie Hartman, confirmed that journalism professor Michael Tracey, communicated with Karr over several months and contacted police.