As a matter of fact, the police investigation threw no light on the mystery. It was learned that Victor Danègre was a dangerous criminal, a drunkard and a debauchee. But, as they proceeded with the investigation, the mystery deepened and new complications arose. In the first place, a young woman, Mlle. de Sinclèves, the cousin and sole heiress of the countess, declared that the countess, a month before her death, had written a letter to her and in it described the manner in which the black pearl was concealed. The letter disappeared the day after she received it. Who had stolen it?

Again, the concierge related how she had opened the door for a person who had inquired for Doctor Harel. On being questioned, the doctor testified that no one had rung his bell. Then who was that person? An accomplice?

The theory of an accomplice was thereupon adopted by the press and public, and also by Ganimard, the famous detective.