As we commemorate the 70th anniversary of the Nuremberg trials, at which selected Nazi leaders were placed in the dock, we must ask some disturbing questions about those who were never tried for their complicity in the world's worst genocide. It would have been impossible to carry out the mass murder of so many people without the complicity of so many governments, groups, and individuals. Perhaps there were too many guilty parties to put them all on trial, but it is not too late to hold the guilty morally accountable for what they did and failed to do.

Seventy years ago, a group of prominent Nazis were prosecuted for war crimes by the WWII allies in the Nuremberg trials. From left to right: In the first row on the stand, Hermann Goering, Rudolf Hess, Joachim von Ribbentrop, Wilhelm Keitel, Ernest Kaltenbrunner. In the second row, Karl Doenitz, Erich Raeder, Baldur von Schirach and Fritz Sauckel.

To be sure, the guiltiest individuals were the Nazi leaders who directly planned and implemented the final solution. Their goal was to in gather Jews from all over the world in order to kill them and to destroy what they regarded as the "Jewish race". They came very close to succeeding, wiping out nearly all of Europe's Jews in a relatively brief period of time. These Nazi leaders had the help of many "willing executioners," both in Germany and in the countries under its control. Among the worst culprits were individual Lithuanians, Latvians, Hungarians, Slovaks, Poles, Ukrainians, and others. There were some heroes among these groups and they are justly remembered and honored. But the number of villains far exceeded the number of heroes.

Then there were the guilty governments that cooperated and helped facilitate the deportations and round-ups. The French government deported more Jews than the Nazis demanded. Other governments, including those of Norway, Holland, Hungary and Austria (which had become part of Nazi Germany), also helped the Nazis achieve their genocidal goal. Bulgaria, on the other hand, declined to cooperate with the Nazi genocide, and its small Jewish population were saved. Denmark too rescued its Jews, many of whom were ferried to neutral Sweden.

There were also the countries that refused to accept Jews who might have escaped the Nazis had they been permitted to enter. These countries include the United States, Canada, and many other potential places of asylum that shut their doors. In the United States and Canada too, there were heroes who pressed their leaders to do more, but for the most part they failed.

Many Arab and Muslim leaders also played ignoble roles, siding with the Nazis and conducting their own pogroms against local Jews. The leading villain in this regard was the Grand Mufti of Jerusalem, who joined Hitler in Berlin and played a hands-on role in sending Jews to their deaths and in keeping the doors of Palestine closed to Jewish refugees.

Could more have been done by Britain and the United States to end the genocide? Could they have bombed the rail lines to Auschwitz and other death camps? These are complex questions that have been asked but not satisfactorily answered since 1945.

There were also the actions of those who pardoned and commuted the sentences of Nazis convicted at Nuremberg, and those who helped Nazis escape prosecution after the war ended. That list too is long and disturbing.

The Nuremberg trials, by focusing narrowly on Nazi leaders and their direct henchmen, implicitly exculpated those who played important, but less direct, roles by their actions and inaction. By their nature, courts are limited in what they can do to bring to justice large numbers of individuals who belong on a wide continuum of legal and moral guilt. But historians, philosophers, jurists and ordinary citizens are not so limited. We may point fingers of blame at all who deserve to be blamed, whether or not they were placed on trial at Nuremberg, or at subsequent legal proceedings.

There will never be perfect justice for those who helped carry out the Holocaust. Most of the guilty escaped prosecution, lived happy lives and died in their beds, surrounded by loving family members. West Germany prospered as a result of the Marshall Plan, and many German industrialists, who had benefited from slave labor, continued to benefit as a result of the perceived needs of the Cold War. The scales of justice remain out of balance. Perhaps this helps to explain why more than 6 million people have been murdered in preventable genocides -- in Cambodia, Rwanda, Darfur and other places -- since the world pledged "never again."

There is, of course, the risk that by blaming all, we blame none. It is important to calibrate the responsibility of those who played very different roles in the Holocaust. This is a daunting task, but it must be undertaken if future genocides are to be deterred.