
Merchants in the Temple by Gianluigi Nuzzi and Avarice by Emiliano Fittipaldi, published last week, are thought to be based on documents from a now-disbanded committee that reviewed Vatican financial affairs in 2013-14.
Vatican spokesman Father Federico Lombardi said Nuzzi and Fittipaldi are suspected of being complicit to the crime of leaking Vatican state secrets, and said more people may be placed under investigation in the future.
The probe by Vatican authorities has already led to the arrest of Spanish Monsignor Lucio Angel Vallejo Balda, who is still in jail, and of Italian PR consultant Francesca Chaouqui, who has been released but remains a suspect.
The leak-based books suggest that Pope Francis' attempts to introduce greater transparency and prudence in Vatican finances are meeting stiff internal resistance, and accuse some top prelates of living in outrageous luxury.
In one egregious case, Cardinal Tarcisio Bertone, former Vatican number 2 under Benedict XVI, is said to have had renovations worth 200,000 euros (215,000 dollars) in his 300-square-metre flat paid by the foundation of a Vatican hospital for children.