Nuremburg Trials: Fair?

As a student, I often find myself confused by the Nuremburg Trials. Hitler committed heinous acts in his treatment of the jews during World War II ,but at the same time Stalin killed huge numbers of his own people and yet because the U.S. and the U.K. were allied with Stalin in World War II there were no war crime trials against Stalin. I often feel conflicted and find it hard to view the trials as fair and objective yet at the same time recognize the horrors and atrocities committed by Hitler's Regime.