It’s rare, but not unheard of, for some people to confess to notorious crimes they did not commit – and suspicions have been raised that John Mark Karr was one such false confessor.

Picked up by police Wednesday in Thailand, Karr readily admitted that he is guilty in the slaying of JonBenet Ramsey. But aside from his confession there is little public evidence linking him to the 1996 crime, leading some experts to speculate that he is either lying or delusional.

“Many high-publicity crimes have these people coming out of the woodwork,” said Elizabeth Loftus, director of the Center for Psychology and Law at the University of California-Irvine.

More than 200 people confessed to the 1932 kidnapping and murder of Charles Lindbergh’s infant son. The 1947 “Black Dahlia” murder – the slaying of aspiring actress Elizabeth Short, who was found naked and sliced in half in a vacant Los Angeles lot – attracted numerous spurious confessions.

And lawyers for the Ramsey family said Friday that a number of people already had confessed to the killing of JonBenet, none of them with enough credibility to attract the attention of law enforcement.

“Often you’re looking at a pathological need for attention,” said Saul Kassin, a psychology professor at Williams College in Williamstown, Mass.

There are countless other reasons that people confess to crimes they never committed. Some people are tricked by police interrogation tactics. Sometimes people confess to take the rap for friends or relatives who have previous convictions. Others simply relent under intense questioning and agree to anything that will end the ordeal.

It is even possible for people to convince themselves, sometimes with help or coercion, that they actually have committed a crime they would have considered unimaginable. In 1988 Richard Ingram, a sheriff’s deputy in Olympia, Wash., confessed to the ritual sexual abuse of his daughters after being convinced by leaders of his church that Satan had compelled his actions and then erased his memory of them.

“People can come to believe that they did things, saw things, experienced things that they didn’t do or see,” said Loftus, who is well known for implanting false memories in subjects’ minds with cleverly constructed psychological experiments.

Psychoanalysts have suggested that some false confessions can be motivated by a subconscious psychological need to be punished for something a person wants to do but hasn’t. Karr has been convicted on child pornography charges and has expressed fascination with young girls in general and the murders of both JonBenet Ramsey and Polly Klaas in particular.

Klaas was abducted from her Petaluma, Calif., home and killed in 1993. Karr moved his family to Petaluma in 2000, and reportedly told authorities he corresponded with Polly Klaas’ killer, Richard Allen Davis.