While Elser was in the bierkeller he noted the stone pillar just behind the speaker’s dais; it supported a substantial balcony along one wall. His rough calculations suggested that a large bomb placed within the pillar would bring down the balcony and bury both the Führer and a number of his chief supporters. The question was how to conceal a device sufficiently powerful to do the job within a piece of solid stonework.
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 of 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.
When the bomb finally went off, it killed eight people and injured 64 others -but Hitler was not one of them . Read the whole story at Past Imperfect. Link