The arrest was the latest blow to the Roman Catholic Church as it struggles to overcome repeated cases of sexual abuse among its clergy. The case was also the worst involving a diplomat since that of former Archbishop Jozef Wesolowski, who in 2013 faced charges of paying boys for sexual acts and downloading and buying pedophile material while he was the Vatican’s ambassador in the Dominican Republic.

The pontiff has declared zero tolerance for the abuse that has plagued the Church for decades, but critics say he has not done enough, particularly in holding bishops responsible for mishandling or covering up misconduct.

The State Department first notified the Holy See in August of a possible violation of laws relating to child pornography images by a member of the Holy See’s diplomatic corps accredited to Washington, the Vatican said in September.

A State Department spokesman said then that the United States had requested that the man’s diplomatic immunity be waived to open the way for a possible prosecution there, but the Vatican had refused. The Vatican did not identify the cleric, but Italian news media reports and an American official familiar with the investigation said it was Monsignor Capella.

He could not be reached for comment; the Vatican said he was being held in a cell in the Vatican’s police barracks.