VIENNA—On May 13, 2015, some 400 attended the unveiling of a plaque dedicated to Gerhard Steinacher, one of Jehovah’s Witnesses, who was executed 75 years ago by the Nazis for refusing to join the German army. The mayor of Vienna’s Meidling District, Gabriele Votava, was the key speaker at the curbside unveiling of the plaque affixed to the outside of the Steinacher family’s former residence in Meidling, Vienna at Lägenfeldgasse 68.

The program bore the theme “I just can’t shoot,” the explanation Mr. Steinacher uttered during his petition for clemency. Those simple words speak volumes about the Christian values Mr. Steinacher held dear, such as Jesus’ words found at Matthew 19:19: “You must love your neighbor as yourself.”

As a youth, Gerhard was a student of the Bible. When he was 17, he decided to become one of Jehovah’s Witnesses. On September 15, 1939, Mr. Steinacher was arrested for conscientiously objecting to military service and for refusing to swear the oath of loyalty to Hitler. After being imprisoned in Vienna for six weeks, Mr. Steinacher was transferred to pretrial detention at the Moabit prison in Berlin, Germany.

On November 11, 1939, the first day of his first hearing, Mr. Steinacher was charged with subverting the war effort and sentenced to death row. He petitioned for clemency based on his religious beliefs. However, on March 2, 1940, the Reichskriegsgericht (Reich Military Court) upheld the death sentence. Four weeks later, on March 30, Mr. Steinacher was executed by guillotine at Berlin’s notorious Plötzensee prison. He was 19 years old.

Following the plaque unveiling ceremony, the event continued at the nearby Volkshochschule Theater. Among the events scheduled was an exhibit that chronicled the Steinacher’s family history. One of the displays featured a small box—found in 1976—containing 28 letters from Ignatz and Luise Steinacher written to their son Gerhard while he was in prison as well as 25 postcards and letters that Gerhard wrote to comfort his parents and express his conviction in their shared faith.

Reporting on the event, an article in Wiener Bezirkszeitung, a weekly Vienna newspaper, describes it as a “remarkable memorial” that brought Mr. Steinacher’s courageous actions “out of the shadows and into the light.” The article further extols Mr. Steinacher by stating: “He was prepared to die for his principles—the very principles that he lived for.”