Christopher Scott, left, and John Mark Karr have confessed to crimes that they could not have committed.

Maximum-security inmate Christopher Scott claims to be the mastermind behind dozens of high-profile felony cases in Western Pennsylvania.

The 27-year-old Penn Hills man has written so many confession letters to local detectives and prosecutors they can recite his words from memory. He promises he will "put out hits" on judges or on victims' families if they don't "come get him" at the State Correctional Institution Mahanoy , Schuylkill County, and let him elaborate.

In exchange for these unsolicited confessions, he always requests a pack of Newport cigarettes and "12 other things," a detail he never explains.

Mr. Scott is serving life sentences for five homicides to which he pleaded guilty, but Allegheny County officials have concluded there is no merit to the grandiose stories he relates in childlike syntax. Like John Mark Karr, the suspect extradited from Thailand and ruled out on DNA evidence in the JonBenet Ramsey homicide, he belongs to a small category of people who voluntarily confess to crimes they have not committed.

Most claim responsibility for cases that garner widespread publicity.

More than 200 people falsely confessed to kidnapping Charles Lindbergh's baby in 1932, about 50 falsely claimed to have slain the Black Dahlia (1940s film star Elizabeth Short) and several falsely confessed to killing O.J. Simpson's estranged wife Nicole Brown Simpson.

"We don't see false confessions in Pittsburgh because we don't have cases that people write books about," said Deputy District Attorney Mark V. Tranquilli. No "voluntary" suspects have made it to trial in at least a decade, he said.

That does not mean toll-free crime hot lines don't get jammed with people confessing to unsolved crimes here and everywhere else. But voluntary fabricators constitute a brief blip on the screen in the justice system. Mr. Scott, with his prolific confession letters, appears to follow the path of most would-be suspects.

Deciphering worthwhile calls from the rest "becomes an administrative chore" for screeners who ask questions to determine whether the person is a legitimate suspect, said Larry Likar, an FBI agent for 23 years who now teaches law and security at La Roche College. Detectives only interview pre-screened callers.

James Morton, assistant superintendent of the Allegheny County police, said in 29 years of investigations he could not recall a single fake confession that passed muster. "We don't release all the facts of the case, so when they come down [to police headquarters] they don't have the details. Only the perpetrator would know those details," he said.

Ron Freeman, a retired city police commander, recalled only 10 or 12 cases in 34 years investigating homicides. "A couple of times somebody came in and said, 'I did it. I killed that person.' But they didn't fit the pattern or the mold," he said. "They just did it for a little attention or sympathy," and then two minutes later they would recant their story.

"When someone walks in off the street and confesses, the police are skeptical and demand corroborating evidence," said Saul Kassin, a distinguished professor of psychology at John Jay College of Criminal Justice, who wrote one of the primary texts on police confessions.

Dr. Kassin identified several reasons for voluntary false confessions.

Some people put themselves in the limelight out of a pathological need for notoriety. Others have an unconscious need to deal with residual guilt for other transgressions.

A third type cannot distinguish facts from fantasy because they are delusional. They have read or heard enough about the case that they've committed the facts to memory. These individuals can sometimes pass polygraph tests because they truly believe they are guilty.

The last type confesses out of a desire to aid or protect the real criminal. For example a child may take the rap for a parent or vice versa. This is the most uncommon scenario, he found.

About 99 percent of the scholarship on false confessions relates to coerced confessions from people who cave in under police interrogation, said Richard Leo, a law professor at University of San Francisco, who has testified extensively on the topic. He said voluntary false confessions are the 1 percent that "almost no one studies."

In cold case homicides, the victims are disproportionately black, Latino and low-income, according to studies by Michael Radelet , a sociology professor at University of Colorado, Boulder. He said people don't usually step forward with false confessions in low-publicity cases.

Unless a person is delusional or guilt-ridden, there is usually some incentive to confess.

The motivations for an inmate like Mr. Scott could be numerous.

According to a spokesman at SCI Mahanoy, Mr. Scott is currently on 23-hour lockdown because of his behavioral infractions. His mother Gwendolyn Harris said several years ago that her son has had mental health problems since infancy. He was born with a brain tumor, which rendered him learning disabled, mentally underdeveloped and impressionable, she said.

He was spared the death penalty when he pleaded guilty to four first-degree homicides in July of 2004. He told an Allegheny County judge he killed Frederick E. Jay Jr., 23, on May 1, 1998 because Mr. Jay insulted Mr. Scott's cousin. He fatally shot Keith "Chubbs" Gales, 19, on May 23, 1999, as he sat in his car. He gunned down 20-year-old Damon Williams, also known as Damon Irvin, outside a Homewood bar on Oct. 9, 1999 and killed Edward L. Owens, 41, a bystander caught in the crossfire between the defendant and a rival gang member, on Nov. 3, 1999.

Mr. Scott was incarcerated on a burglary charge when he confessed to second-degree murder in the 1997 death of his uncle, Milford Scott, in Washington County. After this guilty plea, he wrote police Detective Dennis Logan about the other killings. Police had no leads on any of these homicides.

While his trial was pending and since his last sentencing, he has continued to write to Detective Logan, now an investigator for the Allegheny County District Attorney's office, explaining he played a role in drug rings run by convicted kingpins Terrence Coles and Oliver Beasley and was instrumental in ordering several widely publicized homicides. He continues to ask for cigarettes and visits, but any motivations beyond these are unclear, prosecutors said.

In Mr. Karr's case, some police veterans speculate that he might actually believe he was present when 6-year-old JonBenet was murdered.

Others believe he confessed in hopes of landing publicity.

"Now he's going to do the talk-show circuit and make millions," Mr. Tranquilli said.