The New York Times recently covered the U of M Law School’s release of letters to and from Clarence Darrow.
Robins Kaplan lawyer and Darrow scholar, Randy Tietjen, is responsible for the discovery of a treasure trove of Darrow letters.
You can search the Darrow letter digital archive by year, by people (Helen Keller, Frank Lloyd Wright, Minnesota’s own Sinclair Lewis, and many other luminaries), and by text.
The exchange between Darrow and Lewis is one of many treats in the collection. (Lewis to Darrow in April, 1926: “This noon I talked it all over with Burris Jenkins and we agreed that the lady who tried to assinate Mussolini had a good idea but she would have contributed much more to human progress if she had taken a shot at you instead.” A week later, Darrow responds: “You and that pulpit-pounder Jenkins are a damn fine pair of friends. I could tell the lady where she could do better than taking a shot at me. Anyhow, you will hear from me.”)