ROME -- The Vatican's own police force has arrested a monsignor and a laywoman in its latest probe into the leak of confidential documents.

The Vatican said both people were members of the commission established on Pope Francis' order to investigate the Church's finances. They were being held on suspicion of leaking confidential documents to the media.

A statement released by the Vatican identified the suspects as Spanish priest Lucio Angel Vallejo Balda and Francesca Chaouqui. Chaouqui was released Monday, the statement said, and was "cooperating with the investigation. Balda remained in custody.

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The arrests took place over the weekend but only became common public knowledge on Monday, two days before the slated release of a pair of new books touting new revelations of past misdeeds at the Vatican.

One of the two books is written by Gianluigi Nuzzi, whose 2012 book "His Holiness" contained private documents stolen from Pope Benedict's desk by his butler.

"Regarding the two books in the next days, we clearly state that this time, as in the past, they are the result of 'a grave betrayal of the Pope's trust,'" said the statement released Monday by the Vatican.

It said the books' authors had taken advantage "of a grave illegal act of the delivery of reserved documents" and the possibly criminal consequences would be "studied by the Vatican prosecutor as regards possible further measures."

Both Balda and Chaouqui were members of COSEA (Pontifical Commission for Reference on the Organization of the Economic-Administrative Structure of the Holy See), the now-defunct commission established by Pope Francis with reviewing the Vatican's administrative procedures.

The leaked documents allegedly come from COSEA archives.

A Vatican spokesman, the Rev. Ciro Benedettini, said Vallejo Balda is being held in a jail cell in Vatican City. Chaouqui was allowed to go free because she cooperated in the probe, the Vatican said.

Chaouqui "has furnished the maximum cooperation and deposited documents in support of what she declared," her lawyer, Giulia Bongiorno was quoted as saying by the Italian news agency ANSA. Noting that her client was already back home, Bongiorno added "she is sure she will very rapidly clarify her position."

Bongiorno, who successfully won acquittal for Amanda Knox's co-defendant in an internationally watched murder trial, is one of Italy's top criminal lawyers. She didn't immediately answer phone calls seeking further comment.

Chaouqui, on her LinkedIn profile, describes herself as a communications expert who was the only woman, the only under-55-year-old and the only Italian woman on the pontifical commission.

Opus Dei, the conservative Catholic religious movement, expressed "surprise and pain" over Vallejo Balda's arrest. It described him in a statement as belonging to a priestly society linked to Opus Dei, and added it had no information on the case.

"If the allegation turns out to be proven, it will be particularly painful because of the damage done to the church," Opus Dei's statement said.

While Francis is intent on modernizing the Vatican and making its finances more transparent, the arrests were the latest confirmation that scandal and intrigue still swirl, as they have for centuries, through the largely closed world of the tiny city-state's administrative bureaucracy.

Current and past papacy efforts to clean house at the Vatican have sparked resentment and found resistance in the Holy See's entrenched bureaucracy, a perfect combination of factors to foster leaks.

CBS News' Anna Matranga reports the Vatican is taking the situation very seriously. Holy See officials have contacted Italian authorities to see if there might be punishments of the two authors of these books.

Nuzzi's book is expected to contain transcripts of private conversations between the pope and Vatican officials, designed to reveal the reasons Pope Emeritus Benedict resigned.

Unlike previous similar instances, the Vatican does not see the current leaks as something well-intentioned, Officials believe the leakers are not benefiting the church more broadly by opening up corrupt practices to the world, reports Candida Moss, a University of Notre Dame professor and CBS News contributor.

There is also a danger in prosecuting these two so harshly.

"It's going to look like they're silencing whistleblowers...rather than going after people who were themselves corrupt," Moss says. "It's gonna look like more of the same."