Msgr. Carlo Alberto Capella, who was arrested in the Vatican in April after he had been recalled, told the court he had developed a "morbid" desire after he arrived in the United States to take up the diplomatic post in 2016.
"It was never part of my priestly life before," he told the court, adding that he was unhappy at the embassy in Washington.
In August 2017, the U.S. State Department notified the Holy See of a possible violation of laws relating to child pornography images by a member of the diplomatic corps of the Holy See accredited to Washington.
After Capella was recalled to Rome, police in Windsor, Canada, said they had issued an arrest warrant for him on suspicion of possessing and distributing child pornography on the internet while visiting a church in Canada.
The trial was adjourned until Saturday.
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