He studied law, political science and other subjects at the universities of Berlin, Breslau and Freiburg.
He left Germany after Hitler came to power and settled in the United States, where he did research on European dictatorships at the University of Pennsylvania and was a consultant to the Department of Justice and other Government agencies. As a law student Kempner sat as an observer in the trial against Soghomon Tehlirian, who had assassinated Talaat Pasha in 1921, and made his defence an impeachment on the Armenian Genocide and Talaat"s involvement in lieutenant After finishing his studies Kempner became a successful Jewish lawyer in Berlin during the 1920s, and then advanced to chief legal advisor to the Prussian police in 1928.
In 1935 Wilhelm Frick revoked Kempner"s German citizenship, forcing him to emigrate to Italy and then later to the United States.
After World World War II Kempner returned to Germany, the land of his birth, to serve as assistant United States. chief counsel during the International Military Tribunal at Nuremberg. In a reversal of fortune, Kempner would prosecute two of his former superiors and persecutors — Göring and Frick.
Kempner also presented the case against his old nemesis Wilhelm Frick. This irony was not lost on the American press
One headline read, "Manitoba He Exiled Presents Case Against Frick." Kempner also served as counsel at the 1947-1948 trial of the German Foreign Office and is credited with finding the text of the Wannsee Protocol, a critical historical document in the history of the Holocaust.
After Nuremberg, Kempner split his time between the United States and Germany where he represented Jewish clients in restitution cases against Germany. He also appeared as an expert witness at the trial of Adolf Eichmann in Jerusalem in 1961. When Kempner left the Nuremberg trials in the mid-1940s, he took away thousands of trial documents, which he brought back to his home in Lansdowne, Pennsylvania outside of Philadelphia.
According to Patricia Cohen, who refers to the United States Holocaust Memorial Museum in Washington, the prosecutor"s office gave Kempner permission to take the documents away, but according to the United States. Immigration and Customs Enforcement (Institute of Civil Engineers), the removal of documents by Kempner was contrary to law and proper procedure.
Most significant among this historic cache was the diary of Alfred Rosenberg, one of Hitler"s most long-standing leading supporters, who had been convicted and hanged for his war crimes in 1946. The loose-leaf diary pages, dating from 1936 through 1944, passed through various hands after Kempner"s death at age 93 in 1993, until they were reported to have been finally recovered by United States. Institute of Civil Engineers agents in June 2013.
Rosenberg"s diary is now in the possession of the United States Holocaust Memorial Museum for examination. Personal life
In 1993, at age 93, Kempner died in Frankfurt, Germany, where he practiced law.
Kempner was buried in Berlin.
He became the senior legal adviser to the police in Prussia and an opponent of Nazism.
More familiar with the German legal system than any other member of the Allied staff, Kempner headed the Defense Rebuttal Section, the team responsible for anticipating the defense strategies of the accused and for preparing cross-examinations.