VATICAN CITY (AP) — Vatican prosecutors on Tuesday formally questioned the pope’s butler 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 inside the Vatican gendarmerie building, a four-by-four meter (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 Tuesday that Gabriele had been questioned by the investigating judge Piero Antonio Bonnet on Tuesday 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 leaks 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.

The book’s author, Gianluigi Nuzzi, has said his sources numbered more than 10, and there are questions about whether Gabriele acted alone. He has promised to cooperate with investigators, and Tuesday’s interrogation represented the first time he might have named names.

Papanti-Pelletier, the judge on the tribunal who is not involved in the case, said that while Gabriele was charged currently only with aggravated theft, prosecutors could add on other charges in the Vatican’s penal code, such as being part of a criminal association, receiving stolen goods or revealing state secrets.

Those charges carry a maximum of one to five years.

Gabriele can be held without being indicted for 50 days, with an extension of an additional 50 days if the investigation proves particularly complicated.

Papanti-Pelletier described the Vatican’s legal system, which is based on variations of Italy’s penal and civil codes dating back to the 1800s — with a few modifications. Like Italy, there is the preliminary trial level that is open to the public, an appeals court and a high court. Unlike Italy, though, if a cardinal were to be put on trial, he would only be judged by the Vatican’s high court.

As princes of the church, cardinals can only be judged by fellow cardinals and the pope himself, Papanti-Pelletier said. As such, accused cardinals would skip over the primary and appeals court, which aren’t presided over by cardinals, and be tried directly by the three cardinals who sit on the high court.

As in most countries, the head of state — in this case Benedict — can intervene to pardon someone found guilty. Technically the pope can intervene even before the trial begins, but Papanti-Pelletier said the norm would be for a papal pardon to come after a possible conviction.

Papanti-Pelletier also described Gabriele’s holding facility, saying it wasn’t a cell per se but one of four secure rooms in the Vatican’s main police station. He said Gabriele had access to newspapers but doesn’t have a television in his room. He was escorted to Mass at a chapel inside the Vatican walls on Sunday and eats the same food as Vatican police, he said.

In theory, there could be two possible investigations against Gabriele and any possible collaborators in the papal leaks scandal, because Italian magistrates could be called in to investigate if any Italian citizens were involved or if any crimes were committed on Italian territory.

There also remains in effect in Italy a 1929 provision that criminalizes offending the pope, Papanti-Pelletier noted.

If Gabriele were convicted and not pardoned by the pope, he would serve his sentence in an Italian prison since the Vatican doesn’t have such long-term detention facilities.