Less known is the "Holocaust by Bullets," in which over 2 million Jews were gunned down in towns and villages across Ukraine, Belarus and Russia.
Their part in the Nazis' Final Solution has been under-researched, their bodies left unidentified in unmarked mass graves.
"Shoah," French filmmaker Claude Lanzmann's documentary, stands as the 20th century's epic visual record of the Holocaust.
Now another Frenchman, a Catholic priest named Patrick Desbois, is filling in a different part of the picture.
Desbois says he has interviewed more than 800 eyewitnesses and pinpointed hundreds of mass graves strewn around dusty fields in the former Soviet Union.
The result is a book, "The Holocaust by Bullets," and an exhibition through March 15th at New York's Museum of Jewish Heritage.
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