Sharing the files will allow survivors and victims' relatives to see true images of documents — transportation lists, Gestapo orders, camp registers, slave labor booklets, death books — that evince their tortures and that may have determined whether they lived or died.
With the legal barriers nearly cleared away, the museum will be ready by early next year to begin helping survivors track their history.
''Each day we are losing survivors,'' said museum director Sara J. Bloomfield, and many go to their graves without knowing where or when their loved ones died.
At Bad Arolsen, names fill rooms.
Though now digitized and entered onto a database, the ITS retains all 50 million index cards bearing the names of victims, concentration camp inmates, slave laborers and displaced persons mentioned somewhere in the vast warehouse of papers.
Many are duplications, filed under different spellings, and the cards refer to about 17.5 million people, Jews and non-Jews. The cards alone occupy three cavernous rooms.
Survivors have been waiting for decades to rummage through the archive in search of names.
David Mermelstein, 78, now a Miami resident, will look for his brothers.
''My older brother was with me the whole time,'' from Auschwitz through two other camps. Then they were separated when Mermelstein suffered a work accident. ''About three months before we were liberated, that was the last time I saw him.''
Though the Holocaust and the Nazi reign must be among the most intensively studied 12 years in history, the files could still prove invaluable for new research. ''It won't change the big picture, but no scholars have ever had their hands on this material,'' said Bloomfield. For historians, ''there are going to be some very exciting years ahead.''
Joe White, a specialist on the earliest concentration camps created within weeks of Hitler's 1933 rise to power, hopes to tap the files for new data on privileged groups, like the inmates who acted as overseers known as ''kapos.''
But White, who is with the museum's Center for Advanced Holocaust Studies, also is waiting for the chance to just explore. ''Turning the pages, you find things you weren't expecting.''
Scott H. O'Gara, a teacher of Holocaust studies at Suffolk County Community College in Riverhead, N.Y., said the ITS archive has a rich library of English-language testimony recorded by U.S. Army officers immediately after the war that could throw up new names of SS officers.
''The reports were prepared contemporaneously with the liberation of the camps, and my hope would be that they would prove useful in tracking down some of the perpetrators,'' he said.
When complete, the arrival of the ITS archive will more than double the 40 million pages of records already compiled by the Washington museum, making it one of the world's largest repositories of Holocaust resource material along with Yad Vashem in Jerusalem.
The Israeli memorial already has a database of 3.3 million names of the 6 million Jews slaughtered in the Holocaust and has assembled a team to comb through the newly acquired ITS material for more.
But even with the ITS files, the names of millions of victims are lost forever. The Nazis destroyed much of the evidence of their crimes in the final months of the war, and millions more vanished without a trace in eastern Europe, where record-keeping was less meticulous.
The ITS archive was created to trace the fate of people who went missing during the war and in the chaotic aftermath of the German surrender on May 8, 1945, and to reunite families. Later, survivors turned to the ITS for evidence to support compensation claims for their persecution or property.
But survivors never had direct access to the records themselves. Inquirers submitted applications and often waited years to obtain bare-bones information in a form-letter response.
Missing was the context — the ''feel factor'' of seeing their names as inscribed by wartime German officials, or seeing the orders with perhaps a note by SS chief Heinrich Himmler scribbled in a margin in green ink.
Laymen will be able to browse the archive from computer terminals in the museum, but they still will need professional helpers to find specific information because of the arcane system the Red Cross archivists set up over the years.
But at least they will walk away with copies of the documents on which their names appear ''so that they have something tangible to pass on to their children and grandchildren,'' said Bloomfield.
People hoping to discover the fate of relatives can submit inquiries by the Internet, mail or fax to the ITS, the Washington museum or Yad Vashem. Scholars will have to conduct their research on site.
The ITS in Germany has allowed in few outsiders over the last 60 years, except for the occasional class of schoolchildren. Now it is open to visitors, and while it prefers they make appointments, ''survivors and victims are always welcome,'' says the director, Reto Meister.
Prying open the archive took years of pressure on the reluctant ITS and the 11-nation commission that governs it. Seeing the survivor community rapidly dwindle, the U.S. Holocaust museum began the campaign in 2001, with the State Department later joining the final push.
Opponents argued that the files were subject to strict German privacy laws and that allowing free access by survivors and researchers would distract from the ITS's mission.
The May 2006 decision to amend the 1955 rules was met with repeated delays in implementation. The commission decided each nation must formally ratify the amendments, a process originally expected to take six months but dragged on for 18.
The Greek parliament approved the amendments Oct. 23 — the last of the 11 countries. The archive was officially pronounced open Wednesday after Athens filed its ratification documents in Berlin.
The commission members are the United States, Britain, Germany, Israel, Poland, France, Italy, Belgium, Greece, Luxembourg and the Netherlands.
The key to finding anything is the central name index. Though names are searchable by computer, the index gives a bare outline of personal information and vague indication of how to find the actual documents. No software exists to electronically search and read the documents.
But there will be a guide of sorts to the archive's contents. Over the years the ITS kept an inventory of new documents added to its storehouse. In a few lines, the inventory of more than 21,000 collections gives the date they were registered and a general description. The collections range from a few pages to many thousands.
''For years, the ITS refused to say what was there in the archive,'' said Paul Shapiro, director of the museum's Center for Advanced Holocaust Studies. It was only once the inventory became available that outsiders had their first evidence of its vast scope.
Investing months of work, the museum translated the index of all of the collections and created a search tool for the inventory in German and English and posted it on the Web, Shapiro said. ''We have a responsibility to show the survivors what is there and to demonstrate the scholarly significance of the collection.''
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Associated Press investigative researcher Randy Herschaft in New York contributed to this report.