The Office of Strategic Services (aka OSS) was an intelligence organization set up by the United States and utilized during World War II.
In 1943 an OSS officer had spotted Dmitrij Volkov in Leningrad interrogating prisoners of war (who would later disappear). This was the only sighting of Volkov during the war.
Cate Archer was familiar with this sighting and provided it in her report of Volkov to Mr. Jones and Mr. Smith.
Office of Strategic Services on Wikipedia