The war criminals of the Second World War were put to trial in :

 

 The war criminals of the Second World War were put to trial in Nuremberg.
Key Points The Nuremberg trials were a series of military tribunals held after World War II by the Allied forces. They were most notable for the prosecution of prominent members of the political, military, and economic leadership of Nazi Germany. The trials were held in the city of Nuremberg, Germany, 1 hence the name
Important Points The Nuremberg Trials took place after the end of World War II (1939-1945). They were conducted by the Allied forces, which included the United States, Great Britain, the Soviet Union, and France.
Military Tribunals: These were not ordinary civilian courts but rather military tribunals, established specifically to deal with the unprecedented crimes committed by the Nazi regime.
Prosecution of Nazi Leaders: The primary focus of the trials was the prosecution of high-ranking Nazi officials. 
Additional Information Pittsburgh is a major city in the United States with its own rich history, it was not considered as a location for the Nuremberg Trials.
St. Petersburg, which was indeed a major city in Russia (and previously, the capital of the Russian Empire). However, St. Petersburg was not the location of the Nuremberg Trials.
Gettysburg is in Pennsylvania, USA. The Nuremberg Trials were held in Nuremberg, Germany. These are two completely different locations. 
Time Period: The Battle of Gettysburg took place in 1863, during the American Civil War.