"The fact of the matter is we didn't have much control or any control when dealing with a foreign government," Lacy said. "Hindsight is 20/20."
Lacy said she would not change a thing about how she approached the investigation, except perhaps making a stronger effort to keep details from the media. She said Karr's graphic, detailed claims and his growing fascination with at least one girl in Thailand forced her hand.
"We had probable cause to arrest him," she said. "We also had taken advantage of a forensic psychologist ... who advised that this person was dangerous, this person was escalating."
She added: "We felt we could not ignore this, we had to follow it."
Lacy also said it is difficult to verify any suspect's claims of killing JonBenet Ramsey because every bit of physical evidence in the case has been disclosed to the public over the past 10 years. She noted that several suspects have been investigated in the recent past.
"This guy confessed on numerous occasions in great deal," said Peter Maguire, a deputy district attorney. "He confessed in e-mails, he confessed in telephone conversations ... he admitted it to a police officer. This was a bizarre crime and the person who committed this crime acted in a bizarre way."
JonBenet's father found the little girl's body in the basement of their Boulder home on the day after Christmas 1996. For years, suspicion has focused on either an intruder or the girl's parents, John and Patsy Ramsey.
Karr, who in e-mails and telephone conversations expressed a fascination with JonBenet and Polly Klaas, a murdered California girl, said after his arrest in Thailand this month that he was with JonBenet at the time of her slaying, which he called an accident.
But DNA tests did not match Karr to material found on the girl's body. Prosecutors suggested in court papers that Karr was just a man with a twisted obsession who confessed to a crime he did not commit.
"John Karr inserted himself into this," Lacy said. "I don't have a great deal of sympathy for John Karr."
Wexford Karr, the father of John Mark Karr, had no comment for reporters as he left a courthouse in Boulder Colorado Tuesday, CBS News Denver affiliate KCNC reports.
Lacy has been sharply criticized from the governor and others for detaining and arresting Karr. She estimated costs in the Karr investigation were at least $9,300, and told reporters she has received citizen calls calling for her to be "tarred and feathered" and "run out of town."
"The decisions were mine," Lacy said. "The responsibility is mine and I should be held accountable for all decisions in this case."
Lacy, whose statement was briefly interrupted by a fire alarm at the courthouse, also said investigators surreptitiously took DNA samples from Karr from multiple sites before he was detained. But Karr balked at providing a mouth-swab DNA test, considered the best way to confirm his involvement.
"We couldn't get his consent because he didn't know he was under investigation and we couldn't alert him at that time," she said.
CBS News legal analyst Andrew Cohen said Karr was not the first person to have been checked out and then dismissed as a subject. But the Karr episode generated new leads.
"The investigation into Karr's involvement cost about $15,000, none of which was in addition to Boulder's existing budgets. We have more answers now than we did before," Cohen said. "In the end, it came down to judgment. In the opinion of investigators, Karr was someone worth taking a closer look at. Boulder officials did that and came up empty — an exercise they have gone through many times over the past 10 years. The big difference here is that we all knew about it."
Lacy also said Tuesday that Karr made some "pretty bizarre" claims in hundreds of pages of e-mail conversations with University of Colorado journalism professor Michael Tracey, who alerted authorities to Karr's claims.
But Karr just might have been confessing to an obsession instead of a killing, CBS News correspondent Kelly Cobiella reports. That obsession with JonBenet Ramsey's life and the 6-year-old's death was detailed in four years of e-mails to Tracey.
Lacy conceded authorities were not able to confirm that Karr was in Boulder at the time of the slaying. Investigators said they felt sure of his whereabouts until Dec. 23, 1996, three days before the girl's body was found.