Haaretz journalist Uri Blau was questioned under caution on Tuesday for several hours at the headquarters of the Israel Police's National Serious and International Crimes Unit in Lod, on suspicion being in possession of thousands of stolen classified IDF documents.
Before entering the police station, Blau said he "hoped" the questioning would not take long, but the interrogation is believed to have lasted for over eight hours.
Police are believed to have asked Blau whether the documents were seen by any other parties before they were returned to the authorities.
Before arriving back in Israel from Britain, Blau returned 1,150 classified documents stolen from the IDF's Central Command by Anat Kam, a former army desk clerk and journalist.
It was unclear whether Blau took a lie detector test during questioning.
Law enforcement officials have pointed out that before fleeing the country several months ago, Blau claimed to have returned all of the military documents, a claim which was later proven to be false.
Attorney General Yehuda Weinstein is expected to decide on whether Blau should be classified, as part of an agreement reached between the journalist's lawyers and state prosecutors.