813

"813" is a detective novel by Maurice Leblanc, featuring the adventures of Arsène Lupine, gentleman-burglar, published in June 1910.
summary
813 begins with the murder of then-multimillionaire Mr. Kesselbach, apparently committed by a mysterious L.M., identified by a packet of cigarettes discovered by the room boy. But just as he was about to show it to Mr. Lenormand, a police inspector, he was assassinated. A third assassination then occurs, Chapman, Mr. Kesselbach's secretary, witnessed the scene.