Answer:
It refers to the Holocaust.
Explanation:
The Holocaust was a massive and systematic extermination of millions of Jewish people in concentration camps in Europe during WWII. It was labeled as the "final solution" by the Nazi authorities. Since it was undertaken in secret by the Nazis, many Nazi officials who were judged after the war shielded themselves under the pretext that they did not know about these facts. Other said that, while they knew about some reports on these concentration camps, they thought these reports were exaggerated and that they only finally confirmed them during the trial.
