Erskine refused to write down every crucial element of the treatment, leaving behind a flawed, imperfect knowledge of the steps. Thus, when the Nazi spy Heinz Kruger killed him, Erskine's method of creating new Super-Soldiers died. Captain America, in his first act after his transformation, avenges Erskine. In the 1941 origin story and in "Tales of Suspense" #63, Kruger dies when running into machinery but is not killed by Rogers; in the "Captain America" #109 and #255 revisions, Rogers causes the spy's death by punching him into machinery.