Как ФБР проводило расследование:
The OIG assembled a team of three Special Investigative Counsel, a project director, three OIG Special Agents, two analysts, and a consultant to conduct this review. The team reported directly to the Inspector General.
The team obtained, reviewed, and analyzed more than 368,000 pages of material from the FBI, the Central Intelligence Agency (CIA), the Justice Department, the National Security Agency (NSA), and the State Department. The team also conducted more than 200 interviews in 12 states and the District of Columbia. We interviewed Hanssen's former colleagues and supervisors at the FBI and State Department, as well as family, friends, and acquaintances who knew Hanssen throughout his life. We interviewed much of the operational hierarchy of the FBI's Intelligence/National Security Division (NSD) during the 1979 to 2001 period. In addition, we interviewed CIA and Justice Department personnel who had substantial involvement with the FBI regarding "penetration" matters - that is, investigating whether a foreign intelligence service has infiltrated or recruited agents within U.S. organizations. The team also interviewed Hanssen extensively.
Our full 674-page report is classified at the Top Secret/Codeword level because it contains extremely sensitive classified information regarding sources involved in the Hanssen case and FBI counterintelligence activities. We also produced a 383-page report, classified at the Secret level, which does not contain the detailed information on the sensitive sources that is included in the Top Secret/Codeword version. In addition, we produced this 31-page unclassified executive summary to provide a public summary of the main findings in the more extensive classified reports. We previously provided a copy of all three reports to the FBI for its comments on their factual accuracy and classification, and we made changes where appropriate.