Through his acquaintance with Colonel General
Ludwig Beck, his superior, and then Beck's successor, Colonel-General
Franz Halder, Fellgiebel contacted the anti-Nazi
resistance group in the
Wehrmacht armed forces. In the 1938 September Conspiracy to topple Hitler and the Nazi party on the eve of the
Munich Agreement, he was supposed to cut communications throughout Germany while Field Marshal
Erwin von Witzleben would occupy Berlin. He was a key source for the
Red Orchestra. Fellgiebel released classified German military information to
Rudolf Roessler (codename "Lucy" of the
Lucy spy ring) about
Operation Citadel which allowed Soviet forces to deploy effectively. Fellgiebel was involved in the preparations for
Operation Valkyrie and during the attempt on the
Führers life on 20 July 1944 tried to cut Hitler's
headquarters at the
Wolf's Lair in
East Prussia off from all telecommunication connections. He only partly succeeded, as he could not prevent the informing of
Joseph Goebbels in Berlin via separate
SS links. When it became clear that the attempt had failed, Fellgiebel had to override the communications black-out he had set up. Fellgiebel's most famous act that day was his telephone report to his co-conspirator General
Fritz Thiele at the
Bendlerblock, after he was informed that Hitler was still alive:
"Etwas Furchtbares ist passiert! Der Führer lebt!" ("Something awful has happened! The
Führer lives!"). Fellgiebel was arrested immediately at the Wolf's Lair and tortured for three weeks but did not reveal any names of his co-conspirators. He was charged before the
Volksgerichtshof ("People's Court"). On 10 August 1944, he was found guilty by
Roland Freisler and sentenced to death. He was executed on 4 September 1944 at
Plötzensee Prison in Berlin. ==Memorials==