Vatican prosecutors had accused Mr. Wesolowski of sexually abusing children in the Dominican Republic, where he worked from 2008 to 2013 as the Vatican’s ambassador. They said that he picked up poor boys on the waterfront, paid them for sexual acts and took pornographic photographs of them.

Already defrocked under canon law in 2014, Mr. Wesolowski was facing a prison sentence of up to eight years if found guilty.

The case of Mr. Wesolowski caused an international controversy when it became known that the Vatican, upon learning of the allegations, had spirited him out of the country before he could be investigated by local authorities, and then invoked diplomatic immunity so that he could not face trial in the Dominican Republic.

Then the Vatican decided to try him at home. His trial, which began on July 11, would have been the first case of sexual abuse argued out in a Vatican tribunal, and it became emblematic of Pope Francis’ proactive approach to dealing with the child sexual abuse accusations that have plagued the Roman Catholic Church in recent decades.