On the third day of the process, held under a 19th century Italian penal code, members of the Holy See's small police force said the theft of encrypted documents had compromised some Vatican operations.
They also found instructions that Gabriele had printed on how to hide files in computers and how to use cellphones secretly.
Members of the Corps of Gendarmerie said many newspaper clippings, books and other material seized in the search of Gabriele's apartment showed he was fascinated by the occult, Masonic lodges, secret services, and past Vatican and Italian scandals.
"They (the incriminating documents) were not all in one place. They were hidden among many thousands of pages," policeman Stefano De Santis, one of the agents who searched Gabriele's home, told the court.
Some papers, De Santis said, bore the pope's handwriting and he had marked them "to be destroyed".
The mass of incriminating documents included personal letters between the pope, cardinals and politicians on a variety of subjects.
De Santis said the search turned up "many more" papers than appeared in a book by an Italian journalist who exposed alleged corruption in the Vatican.
"You can understand our unease when we saw these documents. This was a total violation of the privacy of the papal family," he said, using a Vatican term for the pope's closest aides, who serve him in his private apartments.
The trial was adjourned until Saturday, when the prosecution and defense will sum up and the three judges are expected to reach their verdict.
Gabriele, who says he took the documents because he saw "evil and corruption everywhere in the Church," risks up to four years in prison if he is convicted. But the pope is widely expected to pardon him.
Policemen testifying at Wednesday's hearing also rejected Gabriele's accusations, made on Tuesday, that he was mistreated for several weeks after his arrest.