A dead-letter box is a covert location where messages or other items are deposited for retrieval by other intelligence operatives. Also called a dead drop, it is most often used as a means of transferring documents and messages, but can also be used to funnel equipment and money to agents in the field.
Dead-letter boxes can be highly clandestine or in obvious places such as public trash bins, nooks in buildings, and mailboxes that can be incorporated into normal activity. The only requirements are the ability to place items into the receptacle unseen, communication between the two parties regarding drop-off and pick-up, and the ability to elude surveillance.
Although they are one of the oldest tricks in espionage, dead drops remain a useful tool. A successful dead drop requires not only the transfer of items, but also careful attention to counter-surveillance measures. A dead drop is advantageous because it is accomplished without the two parties making contact, thereby rendering surveillance of suspected persons more difficult.
In February of 2001, Robert Philip Hanssen was arrested on charges of espionage after making a dead drop of classified documents in a public park in Vienna, Virginia. Days before his arrest, Federal Bureau of Investigations agents located Russian agents placing a parcel underneath an outdoor amphitheatre in Arlington, Virginia. They retrieved and photographed the package, which contained $50,000, the payment for the documents Hanssen was supposed to leave at the dead drop the day of his arrest. Over the course of 22 years, Hanssen, a veteran FBI counterintelligence officer, used various dead-letter boxes that he created in the New York and Washington, D.C. areas to smuggle information to Soviet (and later, Russian) agents. He was convicted of espionage and conspiracy to commit espionage and sentenced to life in prison. His final dead-letter box, code named Ellis, was underneath the supports of a park foot bridge.