WASHINGTON – Federal authorities have found 400 long-missing pages from a diary kept by a key aide to Adolf Hitler at a small academic publishing house in Lewiston, and Holocaust experts say the find may shed new light on the extermination of millions of Jews during the Holocaust.

The missing diary pages, written by Hitler confidant Alfred Rosenberg, turned up in the possession of Herbert Richardson, the head of Edwin Mellen Press, a small academic publishing house based in Lewiston, the Reuters news service reported on Monday.

A man who answered the phone at Edwin Mellen Press said Richardson would not comment on the diary, which is the second major trove of Nuremberg war crimes trial evidence to be found in Richardson’s possession in the past 13 years.

Federal officials and the U.S. Holocaust Museum are expected to announce the finding of the diary pages at a news conference later this week.

“The documentation is of considerable importance for the study of the Nazi era, including the history of the Holocaust,” according to an assessment of the diary prepared by the Holocaust Museum, which Reuters obtained. “A cursory content analysis indicates that the material sheds new light on a number of important issues relating to the Third Reich’s policy. The diary will be an important source of information to historians that complements, and in part contradicts, already known documentation.”

Rosenberg was a Nazi government minister and Hitler adviser who was convicted of crimes against humanity at the international war crimes trials at Nuremberg in 1946 and subsequently hanged.

According to the assessment Reuters obtained, his diary – which covers the period from the spring of 1936 to the winter of 1944 – offers details on struggles within the Nazi leadership as well as the fascist party’s looting of European art, which he directed.

Rosenberg held several key roles with the Nazi party, heading its foreign affairs operation and editing the party newspaper.

And through it all, he kept a diary that historians will now be able to explore.

The prosecutors at Nuremberg had cited the diary as evidence, but it disappeared once the trials ended.

Reuters said it has long been suspected that Robert M.W. Kempner, one of the Nuremberg prosecutors, brought the diary and other evidence with him after the trials.

In 1999, a vast collection of Nazi documents that Kempner snatched turned up in Richardson’s possession in Lewiston, and he agreed to turn them over to the Holocaust Museum. But the Rosenberg diary remained missing until now.

Law enforcement investigators in Delaware County, Md., said at the time that Richardson obtained the documents by persuading the late Kempner’s aging legal secretary to have Rosenberg’s historical papers transported to the Lewiston publishing house from Kempner’s family home in Maryland.

Federal authorities investigated the moving of those documents to Lewiston, yet no charges were ever filed.

Nevertheless, “it was pretty suspicious,” a detective said at the time.

A lawyer for Richardson, Paul H. Reid of Niagara Falls, told The Buffalo News at the time that the Lewiston academic publisher had done nothing wrong.

“There was no secret about the fact they were moved,” Reid said. “Nobody is trying to hide anything. Nobody is trying to deny the Holocaust Museum of things properly given to them.”