As chief justice inspector at the Laubach courthouse, Kellner had first-hand knowledge of how the Nazis were distorting the laws of Germany. After speaking out for years, Kellner knew that if he continued he would be threatened with internment in a concentration camp, so he took his protest underground. He began a diary he called “My Resistance.”
Over the course of World War II, Kellner wrote 10 notebooks and kept them in a secret chamber in the back of his dining room cabinet. Shortly before his death in 1968, Kellner gave his notebooks to his American grandson, Scott Kellner, with the hope that his eyewitness account would give coming generations “a weapon against any resurgence of such evil.”