Siringo left the Pinkertons in 1907 and wrote Pinkerton's Cowboy Detective in 1910. The Pinkerton National Detective Agency blocked the publication of the book and the final result was A Cowboy Detective in which he was not allowed to use the Pinkerton name or "contains information, business transactions, secrets, names of clients, or any information, knowledge, trade secrets or other matters" pertaining to the Pinkerton National Detective Agency. The financial impact on Siringo was severe however and he grew very bitter towards the Pinkertons. In 1915 he published Two Evil Isms Pinkertonism and Anarchism which recounts a lot more of his assignments during the 22 years he spent with the agency but with very little detail. It did make a point to discuss every illegal, unethical and immoral thing the agency did, painting himself as the only one that would not take that kind of action. It is interesting to note that he put up with that kind of behavior for 22 years and it was not until after his court fight over publication of the Pinkerton's Cowboy Detective that he felt he had to make the world aware of that side of the agency.
In 1927, he published his final autobiography, Riata and Spurs where he revised and republished a lot of chapters from A Cowboy Detective and used the Pinkerton name as well as the real name of clients instead of the fictitious names used in A Cowboy Detective. That apparently only happened in the first edition of the book as the publisher was pressured by the agency to edit future editions.