VATICAN CITY (AP) — There was a time when a Vatican trial could end with a heretic being burned at the stake. Paolo Gabriele doesn't risk nearly as dire a fate, but he and the Holy See face a very public airing over the gravest security breach in the Vatican's recent history following the theft and leaking of the pope's personal papers. Gabriele, the pope's once-trusted butler, goes on trial Saturday, accused of stealing the pope's documents and passing them off to a journalist — a sensational, Hollywood-like scandal that exposed power struggles, intrigue and allegations of corruption in the highest levels of the Catholic Church. Gabriele is charged with aggravated theft and faces up to four years in prison if convicted by the three-judge Vatican tribunal. He has already confessed and asked to be pardoned by the pope — something most Vatican watchers say is a given if he is convicted — making the trial almost a formality. It's the most high-profile case to come to the Vatican tribunal since its creation with the 1929 birth of the Vatican city state. The only other one that comes close was aborted before it began: the 1998 killing of the Swiss Guard commander and his wife allegedly by a disgruntled subordinate never came about because the suspect committed suicide. To be sure, trials are nothing new at the Vatican: In 2011 alone, 640 civil cases and 226 penal cases were processed by the Vatican's judiciary, though only a handful actually came to trial. And that's not counting the marriage annulments, clerical sex abuse cases and other church law matters that come before the Vatican's ecclesial courts. Yet this case will cast an unusually bright spotlight on the Vatican's legal system, which is based on the 19th-century Italian criminal code, and the rather unique situation in which the pope is essentially the victim and supreme judge in this case. The Vatican is an elective absolute monarchy, with the pope having full executive, legislative and judicial authority. He delegates that power through executive appointments, legislative commissions and tribunals. But he can intervene to stop a trial from starting, can pardon someone once convicted and the sentence is issued in his name. Giovanni Giacobbe, the Vatican's appeals court prosecutor, insisted that despite the pope's authority, Vatican judges are wholly independent. "The judges have never received pressure to decide in one direction or another," he told reporters at a Vatican briefing Thursday. "The pope can't tell the tribunal what to do." Gabriele was arrested May 24 after Vatican police found what prosecutors called an "enormous" stash of documents from the pope's desk in his Vatican City apartment. Many of those documents appeared in the book "His Holiness: Pope Benedict XVI's secret papers," by Gianluigi Nuzzi, an Italian journalist whose earlier book on the Vatican bank caused a sensation. Gabriele later confessed to passing the documents off to Nuzzi, hoping to expose what he considered the "evil and corruption" in the church, according to prosecutors. They described Gabriele as a devout but misguided would-be whistle-blower who believed the Holy Spirit had inspired him to protect and inform the pope about the problems around him. "I was sure that a shock, even a media one, would have been healthy to bring the Church back on the right track," prosecutors quoted Gabriele as saying during a June interrogation. Gabriele is being tried along with a co-defendant, Claudio Sciarpelletti, a computer expert in the Secretariat of State who is charged with aiding and abetting Gabriele. While the Vatican legal system will be on display during the trial, so too will be the peculiarities of the Vatican city state itself, the world's smallest sovereign state. Gabriele is both a Vatican citizen and resident of a Vatican City apartment (one of 595 citizens of whom 247 are residents). So the pope is not only Gabriele's former boss, he is also his landlord, his spiritual head as the leader of the Roman Catholic Church and his head of state, not to mention the authority who appointed the prosecutor and the three lay judges who will hear Gabriele's case and decide by a majority if he is guilty. When it was first published in May, "His Holiness" became the most-talked-about book in Italy and the Vatican, 273 pages of secrets about one of the most secretive institutions in the world. It included letters from a Vatican official detailing corruption in the awarding of Vatican contracts, finger-pointing about who was to blame for leaking accusations about homosexual liaisons, and the like. None of the documents threatened the papacy. Most were of interest only to Italians, as they concerned relations between Italy and the Vatican and a few local scandals and personalities. But their very existence and the fact that they were taken from the pope's own desk provoked an unprecedented reaction from the Vatican, with the pope naming a commission of cardinals to investigate alongside the Vatican magistrates. Clerics have since lamented how the episode shattered the trust and discretion that characterize day-to-day life in the Vatican, with bishops now questioning whether to send confidential information to the pope for fear it may end up on the front page of a newspaper. Journalist Nuzzi, for his part, remains calm despite his role as the other key protagonist in the case. "The only thing I can say is that I strongly hope that the trial will unveil the motives and convictions that compelled Paolo Gabriele to bring to light documents and events described in the book," he told The Associated Press this week. Gabriele, a 46-year-old father of three, is being represented by attorney Cristiana Arru after his childhood friend, Carlo Fusco, quit as his lead attorney last month over differences in defense strategy. The Vatican had said the trial would be open to the public, though access is limited and no cameras or audio is allowed. Eight journalists will attend each session and brief the Vatican press corps afterward. There is no indication how long the trial will last, how many witnesses will be called or what Gabriele's defense will be given that he has, according to prosecutors, confessed to taking the documents. Giacobbe noted that in the Vatican legal system, a confession is not enough to convict and that it must correspond with the other evidence uncovered during the investigation. Prosecutors did order a psychiatric evaluation and determined that Gabriele was conscious of his actions, although they quoted the psychiatrists as saying he was unsuited for his job, was easily manipulated and suffered from "a grave psychological unease characterized by restlessness, tension, anger and frustrations." Despite the peculiarities of the Vatican's legal system and the pope's absolute authority over all things legislative, executive and judicial, at least one outside authority has deemed it credible and fair: A federal judge in New York last year dismissed a lawsuit against the Vatican concerning rights to reproduce images from the Vatican library, ruling that the plaintiffs failed to show they couldn't get a fair hearing in the Vatican courts. There has been no such vote of confidence for the Vatican's onetime Congregation for the Holy Roman and Universal Inquisition, the commission created in 1542 that functioned as a tribunal to root out heresy, punish crimes against the faith and name Inquisitors for the church. One of its more famous victims was Giordano Bruno, burned in Rome in 1600 after being tried for heresy.