Dr. Jacob Lestshinsky, was a Polish Jew and the Berlin correspondent of the New York newspaper The Jewish Daily Forward. Lestshinsky was arrested and deported by the Nazis in 1933 for writing gruelpropaganda (he ended up temporarily in the United States, where he spread gruelpropaganda). He was also connected with the Yiddish Scientific Institute of Vilnius (Lithuania) after the war.
Lestshinsky estimated that 5,950,000 Jews were killed by the Nazis.
This is a strange coincidence, as he wrote the following for the June 1938 edition of the Zionist publication Jewish Frontier:
EVERY NATION is morally compelled to face the bitter truth. This article is written not with the intent of bewailing our plight but in order to arrive at a factual calculation of the status of six million Jews in Central and Eastern Europe and of the prospects that exist in the lands of immigration.