Whether it is the hunt for the last surviving perpetrators of the Holocaust, the restitution of looted artworks, or new evidence of the complicity of governments in that immense crime against humanity by Germany and its allies, U.S. public interest in European war crimes has not flagged since the end of World War II.

But the war crimes committed by Japan — including biological warfare, human experimentation, and massacres — have attracted much less attention in the six decades since the war's conclusion, though events such as the publication of Iris Chang's book The Rape of Nanking: The Forgotten Holocaust of World War II in 1997 created spikes in public interest.

Indeed, when the U.S. Congress created a commission to find and declassify records related to World War II war crimes still held by the United States in 1998, the bill was explicitly titled the Nazi War Crimes Disclosure Act. Only a new bill passed in 2000 formally extended the efforts of that commission — renamed as the Nazi War Crimes and Japanese Imperial Government Records Interagency Working Group (or IWG) — to Japan's war crimes.

"As in World War II," says Greg Bradsher, a senior archivist at the National Archives who worked on the project, "we first tackled Germany and then Japan."

Since 1999, the working group has released eight million pages of previously classified documents on Nazi crimes. But this week, the group will release 100,000 pages of newly declassified documents related to Japanese war crimes, along with a new guide to U.S.-held materials on that topic. (A book of introductory essays, Researching Japanese War Crimes, will accompany the release.)...