In the summer of 1944 a delegation of Nazi officials, including Adolf Eichmann, hosted representatives from the International Red Cross at Terezin concentration camp. The visit had been meticulously planned: gardens planted, barracks renovated, streets cleared. Thousands of prisoners were deported eastward to reduce overcrowding. The elaborately staged tour, held on June 23, culminated with a performance by Terezin’s inmate choir. Conductor Rafael Schächter chose to perform Giuseppe Verdi’s “Requiem.”

“When the music stopped,...