The two suspects were carrying fake bond certificates with a face value of some four trillion dollars, and were allegedly hoping to open a line of credit at the Vatican bank. This bank - called the Institute for Religious Works - runs thousands of private accounts held by cardinals, bishops and religious orders all over the world, as well as administering the Holy See's own local payroll.
It's been the subject of enquiries into alleged money laundering. The Vatican, a sovereign state, has been tightening up its international banking procedures after criticism by a European regulatory watchdog body that it's been used as an offshore fiscal haven by unauthorised individuals.
Pope Francis has ordered a complete overhaul of the bank and has set up a detailed enquiry into the transparency of its transactions. Last year the Vatican, for the first time, agreed to cooperate closely with Italian authorities trying to combat any fraudulent use of the bank.
Previously, the Vatican had claimed diplomatic immunity for Vatican bank officials. Pope Francis sacked two of its former directors - both Italians - who now face possible trial on money laundering charges in an Italian court.
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documents given to someone who invests money in a government or company, who promise to pay the money back with interest
the value shown on things like bank notes, coins and stamps
list of people employed by an organisation showing how much each one earns
criminal activity of hiding the origin of money obtained illegally by putting it into other businesses and bank accounts
making rules or laws stronger
group of people who try to stop companies or organisations from doing illegal activities
place where people keep money to pay less tax than in their home country
(here) openness, honesty
special rights that diplomats have which protect them from the laws of foreign countries