Pope Francis has refused to confirm or deny the contents of a bombshell letter by the former Vatican ambassador to the United States, Carlo Maria Vigano. In the letter given to Catholic media outlets, the now-retired archbishop accused the pope of covering up for the sexual misconduct of a U.S. cardinal and urged him to set a good example and resign.

The Pope’s weekend visit to Ireland was dominated by the issue of clerical sexual abuse right up to the end on his return flight to Rome when journalists asked him to comment on Vigano’s letter.

The 11-page document, given on Sunday to Catholic media outlets as the pontiff was on his second day in Ireland, accused Pope Francis of having known for years about the allegations of sexual misconduct by U.S. Cardinal Theodore McCarrick. After credible evidence of abuse of a 16-year-old emerged, Pope Francis last month accepted McCarrick’s resignation, the first of its kind by a cardinal.

Vigano wrote “in this extremely dramatic moment for the universal Church, he must acknowledge his mistakes and, in keeping with the proclaimed principle of zero tolerance, Pope Francis must be the first to set a good example for cardinals and bishops who covered up McCarrick’s abuses and resign along with all of them.”

Vigano, who was ambassador to the United States from 2011 to 2016, said he told Pope Francis about the accusations against McCarrick in June 2013.

A U.S. journalist on the papal plane returning to Rome from Ireland asked the pope to comment on the letter.

Pope Francis said he had read the document and asked the journalists to do the same. He asked them to read the letter and judge for themselves. He said he would not say one word on the contents. He added that he thought the statement spoke for itself. He told those on the papal plane he believed they had sufficient journalistic capacity to be able to reach their own conclusions.

Vigano also named the current Archbishop of Washington, Cardinal Donald Wuerl, who succeeded McCarrick, of having received information about McCarrick from the Vatican. Wuerl’s spokesman flatly denied this.

During a mass Sunday in Ireland, Pope Francis asked for forgiveness for the “scandal and betrayal” felt by the victims of clerical sexual abuse as protesters expressed anger at the church’s handling of the abuse scandals.

The pope also privately met with a group of abuse survivors during his visit.