The motive for the murder in Christie’s Murder on the Orient Express is evidently inspired by a real life crime: the kidnapping and murder of the Lindbergh child. As a member of the Detection Club, Christie, like her fellow authors, shared a fascination with real life crime and, like other members, wove it into her fiction whether as in this case to provide a back story motive or as the main plotline.
The most famous example of this fixation by the club members was the collaborative book The Anatomy of Murder in which they propounded views and solutions to notorious real life crimes. Indeed, Dorothy L. Sayers contributions to that book – an essay on the murder of Julia Wallace (for which her husband was found guilty but subsequently released on appeal on the unprecedented basis that the jury could not reasonably have reached that verdict on the basis of the evidence presented) – is widely regarded as setting out the most plausible explanation for how the murder was committed.
Other famous crime stories have also been based on real life crimes. The earliest example might be Edgar Allan Poe’s The Telltale Heart, published in 1843, which is based on the murder of a retired Captain White by his nephews to inherit his wealth in 1830.
The gruesome 1957 murderer Ed Gein’s mother obsession is a clear inspiration for Robert Bloch’s 1959 Psycho and his methods were replicated by Hannibal Lector in Thomas Harris’s The Silence of The Lambs in 1988.
More recently, Stieg Larsson’s The Girl With The Dragon Tattoo in 2008 draws on the murder of Catrine Da Costa, whose remains were dumped in bin bags in Sweden in 1984.
What, I think, sets these works of fiction apart from mere ghoulish recitals of true crime stories is that they transcend the horrific source material and create something new out of it. There is no disrespect to the victims and, in the final analysis, they must be read purely as fiction.