On 28 April, under cover of a fictional air-raid alarm, some 22,000 prisoners of Gusen were rushed into the tunnels. However, after several hours in the tunnels all of the prisoners were allowed to return to the camp. Stanisław Dobosiewicz, the author of a monumental monograph of Mauthausen and its subcamps, explains that one of the possible causes of the failure of the German plan was that the Polish prisoners managed to cut the fuse wires. Ziereis himself stated in his testimony written on 25 May that it was his wife who convinced him not to follow the order from above. Although the plan was abandoned, the prisoners feared that the SS might want to massacre the prisoners by other means, and the Polish, Soviet and French prisoners prepared a plan for an assault on the barracks of the SS guards to seize the arms necessary to put up a fight. A similar plan was also devised by the Spanish inmates.