Vatican police could be close to arresting another alleged whistleblower, according to reports.

There have been criticisms that the Church is in danger of infringing free speech after an Italian investigative journalist was called in for questioning by Vatican police because of revelations about the Vatican's finances he made in a new book.

Emiliano Fittipaldi this week criticised the Church as "medieval" for interrogating him under a law which applies only in Vatican City State for disclosures made in his book, Avarice.  Another Italian journalist, Gianluigi Nuzzi, is also under investigation by Vatican police for his book, Merchants in the Temple. He was called in for questioning but refused to comply.

Investigators believe an adviser at the Vatican's investment arm may be behind the leaking of some of the documents, which expose waste and extravagant spending on luxuries and are proving highly embarrassing for the Church, according to The Times.

The journalists are being questioned under a Vatican State law passed in 2013 which made leaking documents a criminal offence after the previous Pope's butler, Paolo Gabriele, stole sensitive letters. The law allows four to eight years imprisonment for those who "reveal information or documents whose disclosure is prohibited" and that touch on "the fundamental interests of the Holy See". Regulations covering crimes committed abroad could lead the Vatican State investigation team to request the extradition of Italian national Fittipaldi. 

La Republica reported that investigators are concentrating on uncovering Nuzzi's and Fittipaldi's sources.

Pope Francis has made cleaning up the Vatican a main thrust of his papacy and has often criticised the love of money, which he has described as "the devil's dung". Were a journalist to end up in prison as a result of the latest Vatileaks scandal, his work in courting the international media and his mission to present himself as a modernising, accessible Pope of the people would be seriously, if not irreparably, damaged.  

Fittipaldi told reporters: "I believe that the Italian Republic will oppose any extradition request. It would be an extremely serious precedent."

Meanwhile, as the United Nations Security Council discussed the root causes of conflict, the Holy See's representative Archbishop Bernardito Auza called for international investment in development to help prevent war.

He said there was a need to "break down silos that treat development, peace and security and human rights as separate tasks," Catholic Culture reported.

"Development projects, which could help prevent conflicts, must come first and could substantially lessen future expenses on peacekeeping operations. Resources spent on peacekeeping operations should be shifted to development projects as soon as possible once situations start to stabilise."