Millions of Nazi files that describe in gray, bureaucratic tones the mechanics of mass murder will be thrown open to researchers following an agreement Tuesday by a panel that has kept the archive locked away since World War II.

Once ratified, the decision will give access for the first time to some 50 million files sheltered in a vast archive in the German town of Bad Arolsen, including the registration of concentration camp inmates by the numbers burned on their arms, stacks of crumpled identity booklets and meticulously kept records of executions.

"Bad Arolsen is the most complete file. On many subjects it is unique," said Luxembourg ambassador Paul Mertz, the chairman of the 11-nation International Commission that oversees the archive.

The files also will be available to Holocaust survivors and families of victims whose fate may not be clear.

"This will allow them to bring closure somehow for unanswered questions," said Paul Shapiro, a U.S. delegate affiliated with the Holocaust Museum in Washington D.C. "It's also an insurance policy against forgetting what happened to these people."

After months of negotiations, amendments to two 1955 agreements controlling the archives were initialed by delegates from the 11 countries on the commission. The amended agreements will be signed at a ceremony in Berlin before they are submitted to the individual governments for ratification, Mertz said.

It could take until the end of the year before the process is complete and outsiders will gain access to Bad Arolsen, he told The Associated Press.

As the Holocaust generation dwindled, pressure has been growing for nearly a decade to open the archive, but was thwarted by irreconcilable divisions over the conditions to ease access.

The files hold virtually everything the Nazis recorded on the camps, the prisoners held there and how they operated. Indexed and cross-referenced, they contain 17.5 million names of Jews, homosexuals, the mentally ill, "patients" subjected to cruel medical experiments, millions of people forced into slave labor, and Gypsies, who are also known as Roma.

The card indexes alone occupy three massive rooms at Bad Arolsen, a spa resort in central Germany. The documents themselves, some yellow and crumbling, fill row after row of metal filing cabinets in six buildings.

Experts say the opening could provide new insights into the mechanics of the Nazi extermination campaign and help people discover specific information on what happened to relatives.

The International Tracing Service, the arm of the International Committee of the Red Cross which is the archive's custodian, was founded after the war to trace missing persons. Later, survivors eligible for compensation applied to the archive for documentary evidence of their mistreatment.

Until now, the only way to access the information was to submit a request to the ITS, and await their response.

But the service has lagged behind the number of requests for information, which still flow in by the tens of thousands every year. It now has a backlog of more than 400,000 inquiries about those who disappeared during the Nazi regime.

The breakthrough came last month when Germany agreed to soften its privacy protection rules meant to safeguard the reputations of victims.

Under the changed language, each country will be able to receive copies of the files and will apply its own privacy rules. The countries on the International Commission are Belgium, France, Germany, Greece, Italy, Israel, Luxembourg, the Netherlands, Poland, Britain and the United States.

"We feel tremendous time pressure," said Shapiro. "I only wish we had reached this stage years ago."

The ITS says it has scanned 56 percent of the files since 1999, but it cannot move faster without more funding.

"We have only a restricted budget, and we get the budget only for humanitarian work," said Maria Raabe, spokeswoman of the ITS in Bad Arolsen.

Some of the information on Jewish victims in Bad Arolsen already is duplicated in the huge archives at Yad Vashem memorial in Jerusalem and the Holocaust Museum in Washington.

But Jews were only half of the 12 million people exterminated by the Nazis, and the files in Germany have far more comprehensive accounts of Nazi operations.

Last month, archivist Udo Jost showed an AP reporter an example of documents in the archive soon to be unveiled.

One concentration camp, Mauthausen, in Austria, diligently recorded the deaths of its inmates there, listing them by name, serial and prisoner number as well as the place and date of their birth.

"It also shows how they died," Jost said, showing a copy of the camp's Totenbuch, or Death Book, from 1942 and 1943. "These prisoners were killed every two minutes with a shot to the back of the head."

In a few hours, 300 were executed on April 20, 1942.

"That was Hitler's birthday," he said. "The camp commandant did it as a birthday gift for him."