The biggest criminal trial in the Vatican's modern history, which involves a once-powerful cardinal, opened on Tuesday in a modified courtroom in the Vatican Museums.

Cardinal Giovanni Angelo Becciu is among 10 people accused in a financial scandal involving a loss-making Vatican property deal paid for with donation funds.

The trial follows a two-year probe into the Holy See's flawed €350 million ($412 million) London real estate venture.

The operation exposed the Vatican's opaque financial dealings and its structural dysfunction.

A 487-page indictment released earlier in July revealed huge bank transfers, text messages between collaborators from seized cell phones and bags of money changing hands along with secret meetings in luxury hotels.

The primary defendants are "actors in a rotten predatory and lucrative system, sometimes made possible thanks to limited, but very incisive, complicity and internal connivance," the prosecutors wrote.

Cardinal in the dock

It is the first time in modern history that a cardinal has been indicted by Vatican criminal prosecutors.

Seventy-three-year-old Becciu is the highest-profile defendant in the Church's purchase of the 17,000 square-meter property in the upmarket area of Chelsea. 

Becciu, who was a deputy in the Vatican Secretariat of State, was fired by Pope Francis in September last year and was also stripped of his privileges as cardinal.

He claims that he is an innocent victim of a plot. 

The case against Becciu also includes charges of embezzlement, abuse of office and witness tampering, along with separate allegations over hundreds of thousands of euros of church funds paid to his brother's charity.

It would have been impossible for a cardinal to be in the dock in the Vatican, which has its own judicial system and a prison, until less than three months ago.

But a law changed by Pope Francis now allows Vatican-based cardinals and bishops to be prosecuted and judged by the Holy See's lay criminal tribunal as long as the pontiff signs off on that. 

Earlier, Vatican cardinals could only be judged by their peers in a court of three fellow cardinals.

The trial is likely to be postponed for several months after the first hearings on Tuesday and Wednesday. 

dvv/rc (AFP, AP. dpa, Reuters)