Pope Benedict XVI's butler goes on trial later accused of betraying him by leaking secret documents stolen from his private Vatican apartments.
Paolo Gabriele, 46, was arrested earlier this year and spent two months in custody after the Pope turned detective and ordered a commission of cardinals to track down the source of the leak.
If convicted, father-of-three Gabriele faces up to four years in prison.
The highly sensitive documents alleged details of corruption within the Holy See, outlining how contracts were passed to favoured companies and individuals.
The documents also highlighted power struggles between ambition-hungry cardinals vying for the Pope's favour.
Gabriele was held by Vatican gendarmes after a search of his apartment uncovered a host of personal letters written by the Pope and other officials.
They also found gifts that had been given to the Pontiff: a 100,000-euro cheque written out to Benedict from a South American university, a gold nugget and a 500-year-old book.
During his questioning, Gabriele allegedly insisted he "meant to give back" the items and also wrote to the Pope expressing his "sorrow".
Gabriele also said he had not received "any money or other benefits", stressing he acted to "keep the Holy Father informed of certain facts and events".
Gabriele also told prosecutors he had acted because he had seen "evil and corruption everywhere in the Church" and wanted to stop it spreading.
He said: "I reached the point of no return. I was sure that a shock, perhaps by using the media, could be a healthy thing to bring the Church back on the right track."
The leaked documents were handed to Italian author Gianluigi Nuzzi in secret meetings in cafes close to the Vatican and used in his book His Holiness: Secret Papers Of Pope Benedict XVI. He made sure to burn the originals and any copies that had been made, adding a flavour of Dan Brown to the whole scandal, inevitably dubbed "Vatileaks".
Professor Carlo Cardia, who teaches the history of the Catholic Church at Rome's Universita Tre, told Sky News: "The Catholic Church has seen many scandals in its history but this is one that has grabbed the imagination of the whole world because it involves the Pope's butler, a person who you would expect to be trusted and faithful to the Pontiff.
"I have told my students that Dan Brown didn't need to invent stories about the Catholic Church because there are so many real life ones inside the Vatican - it is made of men who are open to temptation.
"This is a scandal on a human level because it shows the weakness of man but I don't think it will have a profound effect on the Church because it has other more serious problems to deal with."
Gabriele is accused of aggravated theft and his trial will take place in the Vatican courthouse, a building in the Piazza Santa Marta and appearing in the dock alongside him will be IT expert Claudio Sciarpelletti, who has been charged with aiding and abetting the disgraced butler.
A three-man panel of judges will hear the case against the two accused, and there will be no jury.
Only eight journalists will be allowed into the hearing despite hundreds of accreditation requests. There will be no live relay of the proceedings, with no TV crews or photographers permitted.
The tight access has raised questions about whether the Vatican is being totally transparent about the case.
There have been constant rumours in the Italian media since the scandal broke that Gabriele may have been a scapegoat and had the help of senior cardinals within the Church.
One theory is that the documents were leaked to undermine Cardinal Tarcisio Bertone, the Vatican's secretary of state.
Others speculated the leaking was aimed at Monsignor George Ganswein, the Pope's private secretary, who angered the Vatican old guard by giving interviews to Italian glossy magazines.
One source said: "Monsignor George has brought to public attention a role that should be very private and that has resulted in many people getting jealous because they see him as having far too much influence over Pope Benedict."
In an Italian TV interview earlier this year, Gabriele admitted there was "about 20 of us" involved in passing documents outside the walls of the tiny city state and according to prosecution documents posted on the Vatican's website.
Others identified only as "W" and "X" were part of the operation. Their identities are expected to emerge during the trial.
But with a major conference of bishops scheduled to take place at the Vatican in early October, as well as celebrations to mark the 50th anniversary of the Second Vatican Council, Pope Benedict will want the trial over as quickly as possible.
The chance of a pardon has not been ruled out.