crime scene, Lindbergh's interference in the investigation, the ineffectiveness of Hauptmann's counsel, and weaknesses in the witnesses and physical evidence. Ludovic Kennedy, in particular, questioned much of the evidence, such as the origin of the ladder and the testimony of many of the witnesses. According to author Lloyd Gardner, a fingerprint expert, Erastus Mead Hudson, applied the then-rare silver nitrate fingerprint process to the ladder and did not find Hauptmann's fingerprints, even in places that the maker of the ladder must have touched. According to Gardner, officials refused to consider this expert's findings, and the ladder was then washed of all fingerprints. Jim Fisher, a former FBI agent and professor at Edinboro University of Pennsylvania, has written two books, The Lindbergh Case (1987) and The Ghosts of Hopewell (1999), addressing what he calls a "revision movement" regarding the case. He summarizes: Another book, Hauptmann's Ladder: A step-by-step analysis of the Lindbergh kidnapping by Richard T. Cahill Jr., concludes that Hauptmann was guilty but questions whether he should have been executed. According to John Reisinger in Master Detective, New Jersey detective Ellis Parker conducted an independent investigation in 1936 and obtained a signed confession from former Trenton attorney Paul Wendel, creating a sensation and resulting in a temporary stay of execution for Hauptmann. The case against Wendel collapsed, however, when he insisted his confession had been coerced. Another theory is Lindbergh accidentally killed his son in a prank gone wrong. In Crime of the Century: The Lindbergh Kidnapping Hoax, criminal defense attorney Gregory Ahlgren posits Lindbergh climbed a ladder and brought his son out of a window, but dropped the child, killing him, so hid the body in the woods, then covered up the crime by blaming Hauptmann. Robert Zorn's 2012 book Cemetery John proposes that Hauptmann was part of a conspiracy with two other German-born men, John and Walter Knoll. Zorn's father, economist Eugene Zorn, believed that as a teenager he had witnessed the conspiracy being discussed. In popular culture In novels 1934: Agatha Christie was inspired by circumstances of the case when she described the kidnapping of baby girl Daisy Armstrong in her Hercule Poirot novel Murder on the Orient Express. 1981: The kidnapping and its aftermath served as the inspiration for Maurice Sendak's book Outside Over There. 1993: In the novel Along Came a Spider by James Patterson and the film based on the novel, a character takes