For someone with years of preparation, skill, and determination, What an idiot.
He deliberately goes to cross the border, with the BOMB making plans, his communist membership card, and everything needed to convict himself. Then he tells the story whilst there.
He could have easily said nothing, and been denied entry - sent back to Nazi Germany, with likely no questions asked. Or just stayed in Germany, planning his next attempt, no one would have caught him, or figured it out.
Too much Bone instead of Brain.