Who was a little upset that the united states held most of the prisoners tried in the nuremberg trials?

Russia. 
The United states had a major role in bringing the war to an end and at the same time championed the start of the trial of most of the perpetrators of the world War. Although most of the top German military elites that had including Hitler himself committed suicide. Russia felt that it was not fair for the United states to have held most of the prisoners since Russia was also a subject of attack during the war.