In 1919, Keenan became a Special Assistant to the
Ohio Attorney General, with a focus on combating organized crime. He was recruited by
U.S. Attorney General Homer Stille Cummings to serve as a Special Assistant at the
U.S. Department of Justice in 1933. His role was to help address an organized crime wave that was hitting America. During this time, Keenan led prosecutions against notable gangsters during the Depression, including
Machine Gun Kelly and members of the
Barker-Karpis gang. In January 1934,
President Franklin D. Roosevelt appointed Keenan to serve as
Assistant Attorney General for the
Criminal Division. In this role, he was a key liaison between the White House and Congress on issues including legislation addressing kidnapping and organized crime. He played an important role in the drafting of the
Federal Kidnapping Act, which had been prompted by the kidnapping and murder of
Charles Lindbergh's toddler son. In November 1945, President
Harry S. Truman appointed Keenan as Chief Prosecutor for the International Military Tribunal for the Far East, also known as the Tokyo Tribunal. As Chief Prosecutor, he led efforts to investigate and prosecute war crimes committed by Japanese leaders during
World War II. This included prosecuting 28 high-ranking wartime defendants, such as former Prime Minister
Hideki Tojo. == Death and legacy ==