 After graduating from Law School, Thayer began practicing law in New York City under Gen. William Joseph Donovan.He assisted Charles Lindbergh's lead lawyer, Col. Henry Skillman Breckinridge on the famous Lindbergh kidnapping case in 1932, staying at the Charles A Lindbergh residence in Hopewell, New Jersey, until the body of the child was found on 12 May 1932.Bruno Richard Hauptmann was executed for this crime in 1936.