The spokesman said Vatican judge Nicola Picardi has completed "the first phase" of a preliminary investigation and Vatican judge Piero Antonio Bonnet has begun the next step of the inquiry.
Father Lombardi said May 25 that Gabriele, then unnamed by the Vatican, had been questioned by Vatican judges in order to obtain further information.
Gabriele has named two lawyers to represent him during the Vatican investigation and he has already had a chance to meet with them, Father Lombardi said.
The investigation will continue until enough evidence has been collected and then Judge Bonnet will either call Gabriele to stand trial or be acquitted, he said.
A committee of three cardinals Pope Benedict XVI appointed in April to look into the leaks had asked the gendarmes to investigate.
Dozens of private letters to Pope Benedict and other confidential Vatican correspondence and reports, including encrypted cables from Vatican embassies around the world, were leaked to an Italian journalist, Gianluigi Nuzzi. He published the documents in a book, "Your Holiness," released May 17.
In a statement two days later, Father Lombardi called the publication of the letters for commercial gain a "criminal act" and said the Vatican would take legal action. The publication, he said, violated the right to privacy and the "freedom of correspondence" of Pope Benedict, the letter writers and the pope's closest collaborators.
In the book's introduction, Nuzzi said his main source for the texts told him he was acting with a "small group" of Vatican insiders concerned about corruption and a thirst for power within the Vatican. According to his source, Nuzzi said, none of the people giving him documents knew who the others were.