This primary source comes from the Collection DDE-WHOSS: White House Office, Office of the Staff Secretary: Records of Paul T. Carroll, Andrew J. Goodpaster, L. Arthur Minnich, and Christopher H. Russell.
Full Citation: U.S. Note to the Soviet Union - May 6; 5/6/1960; U-2 Incident [Vol. III] [July-August 1960] (2); Alphabetical Subject Files, 1953 - 1961; Collection DDE-WHOSS: White House Office, Office of the Staff Secretary: Records of Paul T. Carroll, Andrew J. Goodpaster, L. Arthur Minnich, and Christopher H. Russell; Dwight D. Eisenhower Library, Abilene, KS. [Online Version, https://www.docsteach.org/documents/document/note-to-soviet-union, May 8, 2024]