VATICAN CITY - Paolo Gabriele, the pope's former butler who was found guilty of aggravated theft, was to be transferred from house arrest to a Vatican prison cell to begin his 18-month sentence.

Because the Vatican's prosecutor decided not to file an appeal, Gabriele would immediately begin serving his prison sentence by order of a Vatican court, said Jesuit Father Federico Lombardi, Vatican spokesman.

"The order will be carried out before the end of the day," he said Oct. 25.

Gabriele, who worked at Pope Benedict XVI's side as his assistant since 2006, will not be allowed to seek any employment at the Vatican in the future, the spokesman said.

Gabriele's violation of the trust of the pope and the privacy of so many people underlines his "incompatibility" with employment at the Vatican, he added.

While the Vatican has begun the necessary paperwork for terminating Gabriele's employment, the Vatican will proceed "with humanity and attention," Father Lombardi told Catholic News Service, saying it will take into consideration the fact that the 46-year-old Italian was supporting a family with three children in an apartment on Vatican property.

He will be detained in one of the recently refurbished prison cells inside the Vatican police barracks.

In a communique issued the same day, Cardinal Tarcisio Bertone, Vatican secretary of state, said Gabriele's crime caused great damage to the pope and to the universal church.

By stealing private correspondence to and from the pope, and other sensitive documents, and by leaking them to an Italian journalist, Gabriele committed "a personal offence against the Holy Father," the cardinal wrote.

His actions also "violated the right to privacy of many people; created prejudice against the Holy See and its different institutions; created an obstacle between the communications of the world's bishops and the Holy See; and caused scandal to the community of the faithful," he wrote.

The affair also "disrupted the serenity" of those who work at the Vatican, he added.

After a Vatican-led investigation, which started in May, and four days of courtroom proceedings attended by a pool of Vatican journalists, Gabriele was found guilty of aggravated theft and sentenced Oct. 6.

Cardinal Bertone said the whole process was carried out with "transparency, equanimity, and in full respect of the rights" of the accused.

The results of the investigation and trial also showed that Gabriele had spearheaded "his criminal project without instigation or prompting by others, but rather based on personal convictions that were in no way held by others," he wrote.

Therefore, the numerous "speculations about some plot or involvement" of other people is "unfounded," the cardinal said.

The secretary of state said it is still possible that Pope Benedict will pardon Gabriele, but such a move "rightly presupposes the reform of the offender and a sincere request for pardon from the Holy Father and all who were unjustly hurt" by his actions.

Gabriele's lawyer had told an Italian newspaper in July that Gabriele had written "a confidential letter to the pope," asking for his forgiveness and telling the pope he had acted alone.

Gabriele had told investigators that he had acted out of concern for the pope, who he believed was not being fully informed about the corruption and careerism in the Vatican.