Source: Timeline
May 27, 1917 Pacelli in Munich sends Cardinal Gasparri in Rome three detailed reports by German Catholic political figure Matthias Erzberger, in Italian, about German war goals, US intervention in the war, and the German press.
Over the next two years, Erzberger serves as a confidential informant and aide to Pacelli within the German Government, until a breach between the two in late July, 1919.
Hundreds of documents by or about Erzberger appear in the German “Pacelli Edition” word-searchable database of Pacelli's Nunciature documents, maintained by the University of Münster, in cooperation with the German Historical Institute in Rome and the Vatican Secret Archive.