* Cardinals look for accomplices of butler, held in "safe room"
* Vatican's number three says book of leaks is "criminal" act
* Special commission has power to question anyone in Vatican (Recasts with Vatican deputy secretary of state)
VATICAN CITY, May 29 (Reuters) - The Vatican on Tuesday denounced the theft of secret papal documents as a "brutal" personal attack on Pope Benedict as a powerful group of cardinals hunted more culprits behind the biggest crisis of his pontificate.
With the crisis over leaks of sensitive documents deepening, the third most senior figure in the Vatican fired a bitter salvo in the Vatican's official newspaper L'Osservatore Romano.
Vatican deputy secretary of state, Archbishop Angelo Becciu said in an interview that the publication of stolen documents in a recent book by Italian journalist Gianluigi Nuzzi was a "criminal" act.
It was the first time the paper has reported on the arrest of Benedict's butler nearly a week ago and it reflected the anger in the Holy See over what is seen as a betrayal of Benedict.
The newspaper also said the butler, Paolo Gabriele, 46, had been in possession of "a large number" of the pope's private documents, the first time the Holy See has come close to publicly quantifying how many documents Gabriele held.
"The act he (the pope) has been subjected to is brutal," Becciu said. "Benedict XVI has seen the publication of papers stolen from his house."
The scandal exploded last week when within a few days, the head of the Vatican's own bank was abruptly dismissed, the butler was arrested and Nuzzi's book was published alleging conspiracies among cardinals, the "princes of the Church".
Gabriele was formally charged with aggravated theft on Saturday when a preliminary inquiry that began with his arrest was upgraded to a formal investigation.
The butler, who was one of the people closest to the pope and is still being held in a "safe room" in the Vatican's police station, will face Vatican magistrates again later this week or next when formal hearings start.
The Vatican says a powerful cardinals commission investigating the scandal, "can decide to hear anyone they think might have information in this case".
"I can confirm that a number of people have been heard or interrogated and naturally this is something that can continue because we are still in the investigative phase," spokesman Father Federico Lombardi told a briefing earlier.
Lombardi denied that any cardinals were suspects in a scandal that has rocked the very top of the Roman Catholic Church since Gabriele's arrest.
Vatican investigators are still sifting through documents found in Gabriele's home, which Lombardi told a briefing likely included printed and electronic material.
"This touched the pope very closely and created a situation of pain. Naturally he wants to know the truth and (determine) the correct interpretation of these events," Lombardi said.
AFFAIR HAS TESTED THE FAITHFUL
While denying reports that the butler was merely a pawn in a larger power struggle among clerics in the Holy See, the Vatican has acknowledged that the affair would test the faith of Catholics in their Church.
Documents leaked to journalists over several months allege corruption in the Church's vast financial dealings with Italian business including infrastructure contracts awarded at inflated prices.
In one example, the Vatican was said to have paid 550,000 euros for a traditional nativity scene in St Peter's Square, thought to be at least double its real value.
Italian newspapers, quoting other whistle blowers in the Vatican, said the arrested butler was merely a scapegoat doing the bidding of more powerful figures, punished because the Church did not dare implicate cardinals behind the leaks.
Becciu said some of what he called "a media flood" about the leaks was part of the media's "underlying hypocrisy" and "fantasy with no relation to reality".
The leaks scandal has touched the Secretariat of State led by Cardinal Tarcisio Bertone, the pope's powerful right-hand man, with Italian media saying the affair appears to involve a struggle between his allies and enemies, reminiscent of Renaissance conspiracies inside the Vatican.
Gabriele's lawyers say their client would cooperate fully with investigators, raising the possibility that he could name other informants.
Critics of the pope say a lack of strong leadership has opened the door to infighting among his powerful aides - and potentially to the corruption alleged in the leaked documents.
Many Vatican insiders believe the butler, who had access to the pope's private apartment, could not have acted alone.
Now known in Vatican statements as "the defendant" - he was until Wednesday night the quiet man who served the pope's meals, helped him dress and held his umbrella on rainy days.
The Vatican's announcement of the arrest of the butler came a day after the president of the Vatican bank, Italian Ettore Gotti Tedeschi, left the bank after a no confidence vote by its board of external financial experts, who come from Germany, Spain, the United States and Italy.
Gotti Tedeschi's abrupt departure was also seen as a blow to Bertone, who as secretary of state was instrumental in bringing him in from Spain's Banco Santander to run the Vatican bank in 2009.
The Vatican bank, officially known as the Institute for the Works of Religion (IOR), was set up during World War Two to manage the accounts of Vatican agencies, church organisations, bishops and religious orders.
It has been involved in financial scandals, most notably in 1982 when it was embroiled in the collapse of what was then Italy's largest private bank, Banco Ambrosiano, with more than a billion dollars in debts.
Banco Ambrosiano's chairman Roberto Calvi was found hanged under London's Blackfriar's Bridge.
In September 2010, Italian investigators froze millions of euros in funds in Italian banks after opening a probe into alleged money laundering involving IOR accounts. The bank denies any illegal activity.
The Vatican is trying to make the IOR more transparent and join an international "white list" of countries that comply with international safeguards against money laundering and fraud. A decision on that application is expected within months. (Reporting By Philip Pullella; editing by Barry Moody)