Emiliano Fittipaldi said he had responded to a Vatican summons to face questioning "because I wanted to understand" the motivations for his prosecution over the contents of his recently published book "Avarice".
The book is largely based on classified documents which were leaked in breach of an anti-whistle-blowing law enacted by the Vatican in 2013 with the blessing of Pope Francis.
"The accusations are crazy," Fittpaldi said. "Such restrictive laws do not exist in any democratic state."
Fittipaldi said he had come away from his interrogation convinced the landmark case would end in a trial of a Spanish priest currently in detention on suspicion of leaking the documents.
"They want to create a precedent, to send a signal to people in the Vatican to ensure there are no other leaks in the future," Fittipaldi said.
His comments came a day after Gianluigi Nuzzi, the journalist who broke the 2012 Vatileaks scandal, said he would ignore a Vatican summons over the content of his latest book, "The Merchants in the Temple."
Accusing Pope Francis of presiding over inquisition-style proceedings, Nuzzi said he had decided not to appear as requested as Vatican law did not guarantee his right to publish news in the public interest while protecting his sources.
Nuzzi and Fittipaldi's books use classified documents to back up depictions of corruption, theft and uncontrolled spending at the Vatican.
They claim charity money was spent on refurbishing the houses of powerful cardinals and that the Vatican bank continues to shelter suspected criminals.
Vatican officials have dismissed the content of the books as either inaccurate or out of date, insisting that reforms instigated by Pope Francis have addressed some, if not all, of the irregularities highlighted.
Angel Vallejo Baldo, a Spanish priest suspected of leaking the documents, is currently in detention in the Vatican pending the outcome of the investigation.
An alleged accomplice, Italian PR executive Francesca Immacolata Chaouqui, is also being investigated but was released from custody after saying she would cooperate with the authorities.
She has since insisted that Baldo acted alone and that the priest had been behind a secret recording of Francis railing against the chaotic state of Vatican finances he inherited on becoming Pope in 2013.
The anti-leaks legislation was adopted soon after Francis took power and was widely seen as a response to Vatileaks, a scandal which saw former pope Benedict XVI seriously undermined by revelations from his butler about intrigue and infighting in the upper echelons of the Church.