Here again Elser proved to have precisely the qualities needed for the job. Knowing that he had a year to prepare, he went to work methodically, obtaining a low-paying job in an arms factory and taking whatever opportunities presented themselves to smuggle 110 pounds of high explosives out the plant. A temporary job in a quarry supplied him with dynamite and a quantity of high-capacity detonators. In the evenings, he returned to his apartment and worked on designs for a sophisticated time bomb.
Past Imperfect, the Smithsonian history blog, has a fascinating feature about Georg Elser, a carpenter who came within eight minutes of assassinating Hilter in 1939. It’s meticulous in describing the care with which Elser approached his bombing. It also questions the ethics of his indiscriminate attempt, even if Hitler was the target.