A statement from Vatican spokesman Federico Lombardi said that Paolo Gabriele was still in custody and been allowed to meet two lawyers of his choice.
The statement said Gabriele benefited from all the judicial safeguards provided for in the Vatican's penal code and investigations were continuing.
It said secret documents had been found at the butler's home in the Catholic Church's city state, but a judge would decide whether he should be prosecuted.
Italian media said Friday that Gabriele, 46, had been working as a butler in the papal apartments since 2006. One source said the pope was "saddened and shocked" by this "painful case".
Gabriele was a member of the small team which works daily in the pope's apartments, but media reports said he was not the only suspect in the leaking of documents, some of which ended up in a new book published a week ago.
His Holiness by Gianluigi Nuzzi reproduces dozens of top-secret and private letters and faxes which were reportedly smuggled out by whistle-blowers tired of the corruption and unhealthy bitterness in the Vatican.
The number of people who have access to the pope's private study is very limited, and includes his butler, four nuns and Benedict's two secretaries, Georg Gaenswein and Alfred Xuereb.
Last month, the pope set up a special commission of cardinals to probe the leaks, which began in January.
The documents have mainly centred on the activities of Vatican Secretary of State Cardinal Tarcisio Bertone and of the Vatican bank, whose head Ettore Gotti Tedeschi was sacked on Thursday.
Tedeschi, 67, was removed by the bank's board for failing to clean up the image of an institution that has come to symbolise the opacity and scandal gripping the Holy See's administration.
Tedeschi, an expert on financial ethics, had also recently been suspected of being one of those behind the leaks.