Otto Eisenschiml (June 16, 1880 – December 7, 1963) was an Austrian chemist, though he spent much of his life in the United States. He invented a window envelope made from one piece of paper. Later he developed a test to detect the presence of fish oil contaminants in vegetable oil. He was president of the Scientific Oil Compounding Company.
He also wrote a book called Why Was Lincoln Murdered? (pub. 1937) in which he propounded his theory that the assassination of Abraham Lincoln was set up by Edwin Stanton, the Secretary of War. The book was popular at the time, but attacked by professional historians as consisting of nothing but "disconnected implication and innuendo" (J. G. Hamilton).
Otto Eisenschiml's book inspired the 1942 Broadway play Yours, A. Lincoln. His theory, or one derived from it, was mentioned by the fictional detective Steve Crosetti in an episode of Homicide: Life on the Street.