During OGPU interrogation Reilly prevaricated about his personal background and maintained his charade of being a British subject born in Clonmel, Ireland. Although he did not abjure his allegiance to the United Kingdom, he also did not reveal any intelligence matters. While facing such daily interrogation, Reilly kept a diary in his cell of tiny handwritten notes on cigarette papers which he hid in the plasterwork of a cell wall. While his Soviet captors were interrogating Reilly he in turn was analysing and documenting their techniques. The diary was a detailed record of OGPU interrogation techniques, and Reilly was understandably confident that such unique documentation would, if he escaped, be of interest to the British SIS. After Reilly's death, Soviet guards discovered the diary in Reilly's cell, and photographic enhancements were made by OGPU technicians.