VATICAN CITY -- Vatican prosecutors formally questioned the pope's butler Tuesday as the investigation into the leaks of papal documents moved into a new phase that could result in a public trial inside the Vatican tribunal over one of the greatest security breaches in the Holy See's recent history.

Paolo Gabriele was arrested May 23 after a significant stash of the pope's documents were found in his Vatican City apartment. He has been held ever since in a secure room in the Vatican gendarmerie building, a 13-by-13-foot room with a bathroom, window, desk, bed and a crucifix on the wall. He is accused of aggravated theft and, if convicted, could face up to six years in prison.

Paolo Papanti-Pelletier, a judge on the Vatican tribunal, told reporters that Gabriele had been questioned by the investigating judge Piero Antonio Bonnet yesterday morning in the presence of the chief prosecutor and Gabriele's two lawyers.

It is the first such formal interrogation and could lead to an indictment or the dropping of charges.

The scandal has convulsed the Vatican for months and resulted in an unprecedented investigation into who was responsible. Gabriele was arrested as part of the criminal probe headed by the pope's personal bodyguard, but a commission of cardinals is also questioning a broad cross-section of Vatican officials and employees, and the Vatican secretariat of state is trying to solve the whodunit as well.

The documents leaked to the press in recent months have alleged corruption in Vatican finances as well as internal bickering over the Holy See's efforts to show more transparency in its financial operations.

The scandal took on greater weight with the publication last month of "His Holiness," a book that reproduced confidential letters and memos to and from Benedict and his personal secretary.

Taken together, the leaks have seemed aimed at discrediting Cardinal Tarcisio Bertone, the Vatican secretary of state, who has been criticized for shortcomings in running the Vatican.

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