Vatican police testifying on Wednesday at the trial of Pope Benedict XVI's former butler said they had found documents in code, research on spying and papers the pope had marked 'Destroy' in his apartment.

More than 1,000 documents -- including copies and originals -- out of 82 boxes of material seized from Paolo Gabriele's flat were considered relevant to the investigation into what has been dubbed the 'Vatileaks' scandal.

The documents were many more than have been leaked and included some signed by the pope himself, along with letters from cardinals and politicians, officers said.

Gabriele, 46, is being tried for aggravated theft and faces up to four years in prison for allegedly leaking confidential documents that revealed claims of fraud and intrigue at the heart of the Catholic Church.

Vatican spokesman Federico Lombardi said a verdict in the trial 'could be expected on Saturday' after prosecution and defence make their closing arguments and Gabriele is given a chance to make a final statement.

"There are more than 1,000 documents of interest including both photocopies and originals and some documents with the signature of the Holy Father," said inspector Silvano Carli, one of four Vatican gendarmes to testify on Wednesday.

Carli said he had taken part in the examination of all the written material seized in Gabriele's apartment behind the Vatican walls, where memory cards, hard disks, laptops and an iPad were also found and are still being analysed.

"There were papers where the Holy Father had written 'Destroy' in German," said Stefano De Santis, one of the gendarmes who took part in the search.

De Santis said the search on May 23 took around eight hours and told the court: "There were many more documents than were published in the book," referring to a book revealing Gabriele's alleged leaks published in May.

"There were also documents in code," he said.

Judge Giuseppe Dalla Torre explained to the court that the code was likely one that is traditionally used in communications by the Secretariat of State, the main administrative body of the global Catholic Church.

"There were dozens and dozens of documents about the Holy Father, about the Secretariat of State and about the other Congregations, about the total privacy and family life of the Holy Father," De Santis added.

"There were letters from cardinals making proposals and asking for advice or responses from the pope to the cardinals," he said.

"All these documents were mixed in with everything else, they were hidden."

He said some of the printed material found but not strictly of interest for the inquiry was about the suspicious death of Italian banker Roberto Calvi -- dubbed "God's Banker" found hanging from Blackfriars bridge in London in 1982.

De Santis said there was also written material about using a concealed mobile phone and how to make videos as well as research on former Italian prime minister Silvio Berlusconi, Italian masonic lodges and world religions.

He said that during the search Gabriele told investigators: "Have you seen how much I like reading? Have you seen how much I like studying?"

Another officer, Luca Cintia, also said: "Some of the documents were signed by the Holy Father and some were in code with 'Destroy' written on them."

Cintia also responded to accusations made by Gabriele on Tuesday that he had been mistreated by the gendarmes during his detention, telling the court that he had been the main person in charge of the butler's incarceration.

"Paolo Gabriele was treated in the best possible way. He was treated with kid gloves. So much so that he thanked us," Cintia said.

Gabriele was held for 53 days following his arrest in two Vatican 'security rooms' at the gendarmerie since the Vatican has no jail.

He alleged the lights were kept on for 24 hours a day during the first three weeks of his incarceration and his eyesight had been damaged as a result.

The accusation has been fiercely denied by the Vatican's spokesman and police have been ordered to investigate the claims.

Gabriele has since been placed under conditions of house arrest.

The trial is taking place under laws that date back to the late 19th century in an area of the Vatican that is strictly off limits to the millions of tourists who visit the world's smallest state every year.

On Tuesday, Gabriele had told judges that he was innocent of theft.

But the ex-butler, whose duties had led him to develop a close relationship with the elderly pontiff, admitted to being guilty of abusing Benedict's trust and said he loved the pope like a son loves his father.

Vatican watchers say he is expected to receive a pardon if convicted.

Gabriele said he was driven to act because he believed the pope was being 'manipulated' and was not well informed about important Church affairs.

He also told the court that he had acted alone, but added that he had many Vatican contacts including cardinals who confided in him.