Top Hitler Aide's Diary Posted Online

A portrait of top Nazi official Alfred Rosenberg, taken Sept. 8, 1937. Pages dated Feb. 2, 1941, from the Rosenberg's diary are displayed at the Holocaust Memorial Museum in Washington, D.C. (Nicholas Kamm/AFP/Getty Images)

The U.S. Holocaust Memorial Museum has published for the first time hundreds of hand-written pages from the long-lost diary of leading Nazi theorist and top Hitler adviser Alfred Rosenberg.

Museum officials said they hope the pages - roughly 400 in total and currently available only in German - will offer new insight into Hitler's inner circle and Nazism's ideological development.

"It has a lot of potential to broaden our understanding of the Nazi past." Juergen Matthaeus, a historian at the museum, told ABC News today. "It will shed light on a key player in the Nazi past and when you look at what was going on at the time, you can see how active his staff was to determine policy."

Rosenberg was an early and highly influential member Hitler's Nazi party. He was the architect of important tenets of Nazi ideology, including racial theory, persecution of the Jews, and lebensraum - the right of "superior" races to displace "inferior" ones from their territories.

"He is really the key player, and this is the one function that is not disputed by any of his peers - he is seen as the keeper of the grail of Nazi ideology," Matthaeus said. "There is an entry in the diary in 1936 where Hitler calls him the 'church father' of National Socialism."

After Hitler was imprisoned following his failed 1923 attempt to seize power in Munich, he made Rosenberg leader of the Nazi movement. Rosenberg then helped lay the theoretical foundation for National Socialism with his book "The Myth of the Twentieth Century," published in 1930.

"He was a very early Nazi and some would claim that he was an even earlier Nazi than Hitler himself," Matthaeus said.

In 1941, Hitler appointed Rosenberg the Reich Minister for the Occupied Eastern Territories, and he is credited with developing the ideological framework leading to the Holocaust. He was found guilty of crimes against humanity at the Nuremberg Trials in 1946 and hanged.

His diary then passed into the possession of Robert Kempner, a German Jewish immigrant to the United States in 1939 and leading prosecutor at the Nuremberg Trials. Publisher Herbert Richardson acquired it from Kempner's family.

Federal agents confiscated the diary from Richardson's upstate New York home last spring after an extensive investigation, but it took more than six months to transfer legal possession of the diary to the U.S. Holocaust Museum, which began publishing its contents on Tuesday.

Acquiring the diary took 17 years, according to Matthaeus.

"The goal here is to really try to make sure that we have, in perpetuity, sources that pertain to the Holocaust," he said.

With the number of survivors rapidly dwindling, Matthaeus said the diary may provide insight into the structure and administration of the Holocaust.

"There is very little that most Holocaust survivors would connect with [Rosenberg]. None would have met him, he was way too removed."

A transcription of the German text is currently under way, and a critical comprehensive edition of all the diary entries is also planned, Matthaeus said.