Fr Lucio Vallejo Balda is still being held in a Vatican jail, while Francesca Chiaoqui was released after cooperating with investigations.
The two worked on a now defunct Vatican committee set up by Pope Francis, which aimed to reform the way the Catholic Church manages its finances.
The Holy See did not confirm what information's been leaked, but says it's a "serious betrayal of trust bestowed by the Pope."
The leaks come before the release of two books later this week, Merchants in the Temple by Nuzzi and Avarice by Emiliano Fittipaldi.
Merchants in the Temple is expected to talk about alleged financial and moral misconduct of cardinals, while Avarice is expected to talk about the alleged financial misconduct of the Catholic Church as a whole.
It has been reported that the Vatican's two arrests are in relation to the two books - both of which regard the Catholic Church and money - but the Vatican has not commented on this.
In a statement, the Holy See said: "It must be remembered that divulging confidential documents is a crime under the criminal code of the Vatican City State (Law IX, art. 10 and art. 116 bis c.p. - passed 13 July, 2013).
"As for the books announced for the next few days it should be said clearly once again on this occasion as in the past, that they are the result of a serious betrayal of the trust placed in certain individuals by the Pope, and, as far as the authors are concerned, of an operation to draw advantage from a gravely unlawful act, i.e. the delivery of confidential documents, an operation, the legal and possibly penal implications of which are currently the object of study in view of possible further measures by the Prosecutor's Office, which will resort, if necessary, to international cooperation."
"Publications of this kind do not contribute in any way to the establishment of clarity and truth, but rather to the creation of confusion and partial and tendentious interpretations.
"We must absolutely avoid the mistake of thinking that this is a way to help the mission of the Pope."
Peter Williams, from Catholic Voices, told Premier's News Hour: "Like any organisation, like any group, and in this case like any state, we have the right to confidentiality.
"It's important that we deal with these sorts of things within house. We already have the right people in place to make sure that any improprieties are dealt with properly, so there's no need for leaking information.
"It's not quite clear why anyone who has continuing doubts about the irregularity or the ethics of financial matters within the Vatican couldn't have talked to someone like Cardinal [George] Pell, who's the Secretariat for the Economy in the Vatican, appointed by Pope Francis to take the lead, as he has done, in reforming the Vatican's financial affairs."
Listen to Premier's Antony Bushfield speaking to Peter Williams on the News Hour:
