BOULDER, Colo. – The Colorado prosecutor admitted Tuesday officials didn’t check out John Mark Karr’s story until after they’d spent $10,000 flying him back from Thailand.

Boulder District Attorney Mary Lacy also acknowledged that critics wanted to see her “tarred and feathered” after Karr’s DNA failed to match stains on slain 6-year-old JonBenet Ramsey’s underwear.

But Lacy said authorities went after Karr because the DNA “surreptitiously” snagged from him wasn’t adequate for testing – and because in e-mails to a Colorado journalism professor he spoke of seducing another young girl.

“We also consulted a forensic psychologist,” Lacy said. “It was his opinion that this person was dangerous.” She added: “I think we did a good job for the community.”

The collapse of the case against Karr means investigators are back to square one in their probe of a slaying that transfixed the nation and stymied cops a decade ago.

Karr said nothing during a 40-minute court hearing where he agreed to be extradited to California to face misdemeanor charges of child pornography possession. He then was sent back to the Boulder County Jail, where his father and brother visited him briefly a few hours earlier.

“This usually takes a couple of days, and with something like this there is no reason to be in any hurry,” Boulder County Sheriff Joe Pelle said.

In a dogged defense of her actions, Lacy said Karr “sincerely believes he killed JonBenet Ramsey.”

“We started immediately upon his detention checking his background, credit card records, financial records,” she said. “The first thing we wanted to do is check whether he was in Boulder” when JonBenet was killed in December 1996.

Investigators took the 41-year-old former schoolteacher’s story seriously, even though specific details of the crime he described in e-mails have long “been out there in the public domain,” Lacy said.

Karr’s claims were later undermined by relatives who said he was celebrating Christmas with them at the time in the South.

When asked if, in hindsight, she would have brought Karr back to the U.S., Lacy said: “I believe we would.”