By Philip Pullella and Naomi O'Leary
VATICAN CITY (Reuters) - Pope Benedict's former butler, facing trial for stealing papal documents, told a Vatican court on Tuesday that he was held in a tiny room with the light on constantly and put under psychological pressure in the first few weeks of his detention.
A judge ordered an investigation of the Vatican police force after Paulo Gabriele made the assertions on the second day of the trial.
Gabriele pleaded not guilty to charges of aggravated theft. He is accused of passing documents alleging corruption in the Vatican on to a journalist.
But he said in his testimony that he considered himself "guilty of betraying the trust of the Holy Father, who I loved like a son".
The session, which also included testimony from Pope Benedict's private secretary, laid bare some of the inner-workings of the Vatican for the first time.
Asked by his lawyer Cristiana Arru if it was true that for the first weeks after his arrest on May 23 he was held in a room so narrow that he could not stretch out his arms, he said: "Yes."
In answer to a question by the judge, Gabriele said:
"For the first 15-20 days the light was on 24 hours a day and there was no switch. As a result my eyesight was damaged."
He also said he was subjected to what he and his lawyer called psychological pressure. On the first night in the room in the Vatican's police station "even a pillow was denied me," he said.
After hearing the accusations of abuse, the president of the three-judge panel, Giuseppe Dalla Torre, told Vatican prosecutor Nicola Picardi to open a file on the issue.
Vatican spokesman Father Federico Lombardi later told reporters that an investigation had been opened.
Lombardi said the room, as small as it may have been, corresponded to international standards and that Gabriele was moved to a larger room as soon as one became available.
Georg Ganswein, Benedict's private secretary, appeared uncomfortable during his testimony as he spoke about daily routines of the papal household and the moment he began suspected Gabriele as the source of the embarrassing leaks.
Gabriele, who appeared calm and smiling during the course of the three-hour session, suggested that important information had been held from the pope.
"At times the pope asked questions about things he should have been informed about," Gabriele said.
It was the first time the 46-year-old servant has spoken publicly since his arrest.
The papers Gabriele admits he photocopied and passed on at secret meetings included letters to the pope in which a senior Vatican functionary expressed concern about improper behavior in the Holy See's business dealings.
The letter-writer, Archbishop Carlo Maria Vigano, was later posted to Washington despite pleading to be allowed to remain at the papal state.
Gabriele said he did not have any direct accomplices but was influenced by others and by a widespread malaise in the Vatican.
The leaks were a blow to the Vatican, which has been eager to clean up its image after a series of scandals involving its bank.
The butler was imprisoned in the Vatican police station while investigators seized 82 boxes of evidence from the apartment where he lived with his wife and three children and from his quarters at the pope's summer residence.
A summary of the inquiry's results released in August showed Gabriele acted because he saw "evil and corruption everywhere in the Church" and felt the pope was not sufficiently informed.
The trial was adjourned until Wednesday morning.
(Editing by Angus MacSwan)