Records kept on Monroe, many of which were filed under "Foreign Counterintelligence," have intrigued many who have sought to learn more about the film star, including those who investigated her death.
In connection with the 50th anniversary of Monroe's death on 5 August, The Associated Press has attempted under the Freedom of Information Act to obtain the most complete record of the bureau's monitoring of Monroe.
Nearly nine months later - after several requests and an appeal - obtaining a more complete record of how the FBI investigated Monroe in the months before she died have been stymied by an effort to simply find the files.
The FBI says it no longer has the files it compiled on Monroe; the National Archives - the usual destination for such material - says it doesn't have them either.
Finding out precisely when the records were moved - as the FBI says has happened - required the filing of yet another, still-pending Freedom of Information Act request.
The most recent version of the files, all heavily redacted, is publicly available on the bureau's website, The Vault, which periodically posts FBI records on celebrities, government officials, spies and criminals.
Monroe's star power and fears she might be recruited by the Communist Party during the tenure of longtime FBI Director J. Edgar Hoover led to reports being taken on her activities and relationships, including her marriage to playwright Arthur Miller.
Monroe's file begins in 1955 and mostly focuses on her travels and associations, searching for signs of leftist views and possible ties to communism. The file continues up until the months before her death, and also includes several news stories and references to Norman Mailer's biography of the actress, which focused on questions about whether Monroe was killed by the government.
That mention intrigued the man who performed Monroe's autopsy, Dr. Thomas Noguchi. While the DA investigation concluded he conducted a thorough autopsy, Noguchi has conceded that no one will likely ever know all the details of Monroe's death. The FBI files and confidential interviews conducted with the actress' friends that have never been made public might help, he wrote in his 1983 memoir "Coroner."
"On the basis of my own involvement in the case, beginning with the autopsy, I would call Monroe's suicide 'very probable,'" Noguchi wrote. "But I also believe that until the complete FBI files are made public and the notes and interviews of the suicide panel released, controversy will continue to swirl around her death."