Hofacker's main activity in relation to the events culminating in the attempted assassination of Hitler at the Wolf's Lair on 20 July 1944 consisted of acting as a secret liaison between his cousin and another plotter in occupied Paris, General Carl-Heinrich von Stülpnagel, France's military governor, to whom he was personal adviser. Hofacker assessed the chances of the coup attempt as "only ten percent". He had a point of introduction to Field Marshal Erwin Rommel as he considered his father something of a hero, having served under him in World War I. He tried to draw him into the plot to rid Germany of Hitler, but although Rommel gave his backing to the conspiracy he did not agree that he should be killed
On 26 July 1944, Hofacker was arrested in Paris, taken to Berlin Gestapo headquarters where, according to William Shirer in "The Rise and Fall of the 3rd Reich", he was horrifically tortured and gave up the name of Erwin Rommel stating that Rommel said to "Tell the people in Berlin they can count on me". This was support for the conspiracy to overthrow Hitler, not to kill him- but this made no difference to Hitler who ordered the forced suicide of Erwin Rommel and false hero's funeral. ] The torture confession was taken down and Hofnacker was put on trial before the Volksgerichtshof. He was found guilty of treason and sentenced to death. He was hanged at Plötzensee Prison in Berlin.