The investigators say they were reluctant to believe McGraw at first, but at the time he was the best lead they had. McGraw listed an impressive array of hardware allegedly used by the killers, including such glamorous weapons as a plastic Glock pistol and a 9-millimeter Beretta, but none of it matched the ballistics information the police had. One detective noted that McGraw gave investigators nothing of consequence, but at least he was giving up names. And in a case that had come under international scrutiny, it was impossible for the investigators to ignore any leads.

So the other Tucson suspects were picked up. And some of the things they told police were extremely troubling.

The statements of both McGraw and Dante Parker, for instance, mention the loot from the temple being carried out in a black bag. And detectives say Parker accurately described a piece of jewelry they didn't even know was missing until they checked with the victim's family after Parker was arrested and charged with the murders.

There were problems, but there are always problems with confessions, investigators say. As Agnos points out, the hours of denial, the spotty details, the sloughing off of blame and the confusion are all part of the classic matrix of detective-criminal interaction.

There's a classic interviewing process that one goes through in dealing with a criminal," Sheriff Agnos says. I will tell you, to be a good police officer you have to be a very good poker player. You have to know when to bet, when to raise, when to check, when to pass, and, as the song by Kenny Rogers says, you gotta know when to hold 'em and know when to fold 'em, because these criminal suspects are experienced individuals and they will take you around in circles. You have to go kind of where they take you."

And now Leo Bruce, Mark Nunez and Victor Zarate are taking him to court.

PEOPLE HAVE BEEN aware of the phenomenon of false confession for hundreds of years.

In England in 1660, William Harrison disappeared, and his servant, John Perry, was sent to look for him. When Perry failed to return to his own home that evening, the authorities became suspicious. Perry was confronted with a bloody hat allegedly belonging to his master. After several days of intensive questioning, Perry broke down and confessed to murdering Harrison. His statement also implicated his brother and mother in the crime, and, on the basis of that statement alone, all three were convicted and executed.

Two years later, William Harrison reappeared. He said he had been ambushed, kidnaped and sold into slavery in Turkey. Eventually, he escaped and returned home. Perry's Case," as the incident has come to be known, is the seminal case from which the body of British and American law surrounding confessions proceeds. Soon after Harrison's reappearance, some English courts began to require proof of the victim's death-the corpus delicti requisite familiar to readers of Erle Stanley Gardner-as corroboration of a murder confession. Though the rule was never applied universally in Great Britain, it has been adopted by all American jurisdictions save Massachusetts.

Gisli Gudjonsson was a police detective with the Reykjavik Criminal Investigation Unit in his homeland when he had his first experiences with false confessions. One case involved the murder of an elderly woman who was killed when she apparently surprised a burglar in a house she was watching for friends who were traveling abroad.

Because murder is relatively rare in Iceland," Gudjonsson says, it was well-publicized in the papers, and soon a man came to the police station and said he had committed the killing. He was interviewed and gave an account that did not coincide with the facts of the matter, so we decided his confession was undoubtedly not genuine."

Later, a well-known television personality was arrested and convicted of the woman's murder-he presumably killed the woman because she, and anyone else in Iceland, could have identified him.

A second case involved a man Gudjonsson describes as a well-known thief." After the man left the home of a woman he had been drinking with, she noticed her purse was missing and called the police. When Gudjonsson apprehended him, the man eventually said, All right, I must have done it." Gudjonsson says the thief said he could not remember taking the purse, but that he had a history of blackouts and he thought he must have taken it. Later, the woman found the purse, which had slipped behind a settee.

Nevertheless, he confessed to the crime because he thought he must have done it, not because he had any memory of doing it," Gudjonsson said.

IN ADDITION TO ITS guarantees of due process and against double jeopardy, the Fifth Amendment provides that no person can be compelled in any criminal case to be a witness against himself." But the concept of compulsion is a slippery one, and surely an innocent person would not confess unless he or she was somehow compelled to do so. Gudjonsson's research, however, indicates that normal, accepted police procedure can sometimes result in normal" people-that is, people who are not mentally debilitated-confessing to crimes they did not commit.