He also alleged he was mistreated during his 53-day detention in the Vatican, claiming he was initially held in a "security room" where he could not stretch his arms and with the light on 24 hours a day for up to three weeks.

The Vatican ordered an investigation into the claims but spokesman Federico Lombardi said the dimensions of the cell were in line with international standards and said Gabriele's charges "raise a few queries".

The ex-butler told judges in the tiny state's 19th-century courtroom that he had been driven to act because he believed the pope was being "manipulated".

"What really shocked me was when I sat down for lunch with the Holy Father and sometimes the pope asked about things that he should have been informed on. It was then that I became firmly convinced of how easy it was to manipulate a person with such enormous powers," Gabriele told the court.

Gabriele was repeatedly interrupted by the judge as he tried to recount details of his network of contacts in the Vatican and his personal motivations.

When his lawyer asked about particular incidents he was upset about, judge Giuseppe Dalla Torre said: "It's irrelevant. We have to stick to the charge."

Gabriele also told the court he had acted alone without any accomplices but had many contacts, including two cardinals in the Vatican - where he said there was "widespread unease" and where many people shared their problems with him.

The father of three, who is under house arrest, is accused of leaking hundreds of memos that reported fraud and intrigue among top Vatican figures.

If convicted of aggravated theft, Gabriele faces up to four years in jail.

Gabriele has not entered a plea. Although he has admitted leaking the documents, his confession is not legally considered definitive proof for a conviction because he could have lied to protect fellow whistle-blowers.

At the start of the trial on Saturday, Gabriele suffered a series of setbacks when judges turned down his lawyer's requests to strike down his indictment and throw out the case because of rules on papal secrecy.

Judges also declined to include in the trial a top secret report on the "Vatileaks" scandal compiled by a committee of cardinals appointed by the pope who interviewed dozens of people in a parallel investigation into the leaks.

The first hearing also revealed that Vatican gendarmes had seized 82 boxes of material from Gabriele's service apartments in the Vatican and at the pope's summer residence and installed a camera on the landing of his Vatican flat.

In a February interview with Gianluigi Nuzzi, the Italian journalist to whom he is accused of leaking the documents to, he expressed frustration with a culture of secrecy in the Vatican - from the mysterious disappearance of the daughter of a Vatican employee in 1983 to a hushed-up murder by a Swiss guard in 1998.

"There is a kind of omerta [silence in Mafia terminology] against the truth, not so much because of a power struggle but because of fear, because of caution," Gabriele had said.

Gabriele said he was inspired by the Holy Spirit to reveal intrigues behind the Vatican walls so as to help the pope clear out corruption from the heart of the Catholic Church.

"There is a lot of hypocrisy, this is the kingdom of hypocrisy," he said.

Gabriele also said he was aware of the consequences of his actions. "Being a witness to truth means being ready to pay the price," he said.