On the morning of Monday 15 October 1894, a trainee officer in the French Artillery, Captain Alfred Dreyfus, reported to a meeting that he had been ordered to attend at the Ministry of War in Paris. Originally told that this was part of an inspection of other trainees, Dreyfus was surprised to be met by another officer and three unknown civilians, who were later revealed to be senior officers in the police and army intelligence service. After obeying a mysterious request to write a letter dictated from a document by the other officer, Dreyfus was then arrested for high treason.

The charge related to the sale of French military secrets to the German military attaché in Paris. A memorandum recording this sensitive information was recovered from a waste bin at the German Embassy by one of the many domestic workers employed as agents by French intelligence, and passed back to the Ministry of War on 26 September. The degree of detail in the memo caused considerable alarm among the French General Staff, and an urgent investigation was set in place to trace its source. With few leads to go on, the investigators decided to narrow their search based on a profile of the kind of officer that would have access to such information (making, as it later turned out, a number of unwarranted assumptions as they did so).