When John Mark Karr was picked up in Thailand Aug. 16, police thought they finally had a break in the 1996 murder case of then 6-year-old JonBenet Ramsey.

After all, Karr publicly said "No" when asked if he was innocent.

But on Monday, after finding the 41-year-old school teacher’s DNA did not match the DNA found on the little girl’s underwear, Colorado authorities said they weren't going to charge Karr with the murder.

Why would anyone confess to a crime he didn't commit?

While there is no "typical" false confessor, psychologists who study the phenomenon speculate that Karr was looking for attention -- and that he had fantasized so extensively about JonBenet, even claiming that he loved her, that the line between fantasy and reality, for him, has blurred.

For some other false confessors, it may simply be the thrill of the lie -- they love duping people.

The Drive for Attention

"Some false confessors have a pathological need for attention," Saul Kassin, Ph.D, a distinguished professor of psychology at the John Jay College of Criminal Justice in New York and professor at Williams College in Williamstown, Mass., says to explain confessions like Karr’s.

“That is what everyone is speculating in the Karr case," he says. "The pathology is such that that need predominates. And everything else fades into the background." Even the risk of prison or death.

"They are driven by the limelight," adds Eric Hickey, PhD, professor of criminal psychology at California State University, Fresno, and director of the Center of Forensic Studies at Alliant International University, Fresno. And, sometimes, financial gain. "They want the notoriety, the attention, but they also plan on making money. Some people may have in mind when they confess, maybe a book [will come out of this]."

Other confessors are angry and want to be heard, Hickey says. "They want a voice. They don't feel like they have a voice."

Thin Line Between Fantasy and Reality

A blurring of fantasy and reality can also play a role in a false confession. "We know that Karr has immersed himself in the facts of this case," Kassin says. News reports describe how Karr emailed a Colorado professor repeatedly, talking about his involvement in the murder.

"He wanted to be connected to JonBenet so badly," Hickey says. "Maybe he thought about it so much he fantasized himself into believing it."

When people repeatedly imagine an event, over and over, they become less certain about whether it is real or not, Kassin says. "The memory research on this is clear -- it's called 'imagination inflation.’"

Complicating Karr’s situation, Hickey says, is that he appears to be a man "with a lot of conflict, questions about his own sexual identity."

The Thrill of the Lie

Then there are people who just get a thrill out of lying, says Cynthia Cohen, Ph.D, a research psychologist and jury consultant based in Manhattan Beach, Calif. Law firms and corporations hire Cohen for her expertise on deception.

"This is what lying expert Paul Ekman [a renowned expert in the field] calls 'duping delight,’” Cohen says. “In putting something over on someone, they get a thrill.

“It's almost like someone who likes to do bungee jumping. Someone who has duping delight gets excitement from telling a lie and having someone believe it," she says. "Maybe they got rewarded for their tall tales in childhood," says Cohen. Perhaps their friends or even their parents thought the behavior was cute.

The History of False Confessions

Kassin says there are no accurate numbers on how prevalent false confessions are, but the phenomenon is not new.

In 1932, after aviator Charles Lindbergh's son was kidnapped, 200 or so stepped forward to confess, Kassin says.

These days, sophisticated DNA technology can prove or disprove a suspect's story, making it easier to spot a false confession, he says.

But even with modern technology, finding out a confession is a lie can take time. Kassin cites the 1989 case of the Central Park jogger -- a woman raped, beaten, and left for dead. Within 48 hours, Kassin recalls, five boys had been arrested.

The boys were interrogated, confessed, and then sent to prison--despite the vehement contention of their parents and supporters that the confessions of the teen suspects had been coerced. "In 2002, someone stepped forward from prison to confess," Kassin says. "He was the real rapist."

Voluntary or Involuntary Confessions

Why the five boys confessed isn't known, Kassin says, but the police interrogation may have played a role.

Kassin calls such false confessions, which come after police interrogation, involuntary. He differentiates between them and voluntary false confessions, in which someone walks in off the street and confesses to police.

"Voluntary confessions tend to drop out of the [criminal justice] system," Kassin says. "More often than not, when police are confronted with a voluntary confession, they are inherently skeptical. And they demand corroboration."

The involuntary false confessions, he says, are the ones that "haunt the criminal justice system."

They're often produced, Kassin says, after intense questioning of people who are isolated and often sleep deprived. Suspects somehow decide it might be easier to confess even though they know they are innocent.

"Everyone has a breaking point," says Kassin. "When people are under stress, they become incredibly short-sighted in their decision making." They're thinking only: ‘I gotta get out of here’ -- not about long-term consequences such as jail time.

And, according to Kassin’s research, after enough pressure from interrogators claiming to have proof they’re guilty, some suspects begin to doubt their innocence themselves.

By Kathleen Doheny, reviewed by Louise Chang, MD

SOURCES: Saul Kassin, PhD, distinguished professor of psychology, John Jay College of Criminal Justice, New York; professor, Williams College, Williamstown, Mass. Eric Hickey, PhD, professor of criminal psychology, California State University, Fresno; director of the Center of Forensic Studies, Alliant International University, Fresno. Cynthia Cohen, PhD, research psychologist and jury consultant, Manhattan Beach, Calif.