World War I was over for several years before there were any answers, and they came as part of a lawsuit brought against Germany by the companies that had experienced mysterious explosions after 1914. The charge was sabotage, engineered by a cadre of secret agents who had come to America shortly after war broke out in Europe, as the "diplomatic staff" of German Ambassador Johann Heinrich von Bernstorff. One German agent, Capt. Franz von Rintelen, who called himself "The Dark Invader," promoted widespread use of the "pencil bomb." This ingenious time-released incendiary device fit neatly into a small tube, no bigger than a cigar. It was easy to hide and could be designed to blow up in hours or even days after it was planted.