As president of Shomrim, a fraternal order of Jewish New York City police officers, he became famous in 1938 when Fiorello H. La Guardia picked him to lead a special squad whose job was to safeguard visiting officials from Nazi Germany and guard the German consulate.
[1] A popular belief was that La Guardia's decision to appoint Finkelstein and the other Jewish officers was inspired by actions taken by Theodore Roosevelt, when he was New York City Police Commissioner, who assigned 40 Jewish police officers to protect, and make look "ridiculous", Hermann Ahlwardt, when he gave an anti-semitic speech in New York.
[2] While a popular story published by the Times during a later period of anti-Nazism, this story is not supported by news articles of the time and in fact the names of officers printed during Ahlwardt's 1895 visit are Anglo or Irish names, such as Cartright and O'Brien, not generally used by Jews.
However, after being told "that he would be required to face charges of accepting irregular bail bonds", he committed suicide.
[6] Finkelstein's experience guarding Nazi diplomats in New York served as the basis for a character in the 1939 Broadway play Margin for Error by Clare Boothe Luce.