JAKE ROSSEN wrote at mentalfloss.com on June 25, 2017:
“Arsenic, cyanide, even nicotine: No toxic substance escaped the attention of Agatha Christie, the celebrated mystery writer of over five dozen novels. While her fictional victims were always subject to being stabbed, shot, or pushed off a cliff, the primary method of disposal was poison. Slipped into nightcaps, eye drops, even seeping from wallpaper, a variety of fatal chemicals provided her characters with mysterious ailments and puzzling clues that made for ideal murder material.
Christie’s assured handling of poisons came from first-hand experience with pharmaceuticals. She had volunteered to become an apothecary’s assistant at a hospital during both World Wars, acquiring a vast knowledge of drugs she then utilized in her detective fiction. With few exceptions, her descriptions of dosages, reactions, and mortality rates were rivaled only in specialist texts.
While this attention to detail was normally celebrated, there was one instance when a hysterical news media—and even Christie herself—became alarmed that she may have taken things too far.
The book in question was The Pale Horse, a novel about a group of contract killers using thallium, a heavy metal discovered in 1861 but largely obscure until Christie wrote about it. The real-life murderer was Graham Young, who was sentenced to life in prison for using thallium to poison an untold number of people, killing three. His experiments began in 1961, while he was just 14 years old. The Pale Horse, the first and only time Christie used thallium as a plot device, was published the same year.
At Young’s trial, pathologist Hugh Molesworth-Johnson said Christie’s descriptions of the drug were so accurate they rivaled the reference books of his profession, and the news media began to speculate about whether the boy had been influenced by the work. Had Christie’s fiction turned into Young’s horrific fact?…
…Young was sentenced to life in prison in 1972. During his well-publicized trial, much was made of Christie’s use of thallium in The Pale Horse and its relative rarity as a murder weapon. A month after his sentencing, Christie, then 81, expressed concern she could have given Young ideas. Her husband, Sir Max Mallowan, told reporters he wondered if “this fellow read her book and learned anything from it.” The Daily Mail published a list of similarities between Young’s victims and Christie’s descriptions. They could hardly resist the implication that the author had created a literal monster.
During Young’s 1972 trial, a pathologist testified that Christie’s book was the only source outside of reference books where such specific and accurate information about thallium could be found. Young himself never made any conclusive statement about The Pale Horse; it’s possible his knowledge came from studying medical texts during his library days as an adolescent.
Young, however, couldn’t seem to escape his curious connection with Christie. When a nurse was reading the book in 1977 and recognized symptoms of thallium poisoning in a patient being treated in her ward, Scotland Yard suggested that doctors interview Young because he was undeniably an expert on the substance—and happened to be serving his life sentence right next door to the hospital, in Wormwood Scrubs Jail. It wasn’t necessary, though; tests confirmed thallium. The patient was treated using a compound known as Prussian Blue, which binds to the metal and excretes it. She survived. Young died in 1990 of a heart attack at the age of 42.
It was not quite the end of thallium as a source of misery. In 2005, a 16-year-old in Shizuoka, Japan, used it to try to poison her mother, who fell gravely ill. While in the hospital, the girl—whose name was withheld from media—attempted to poison her again. She eventually confessed, with a judge sending her to reform school.
During their investigation, authorities discovered a blog that documented her mother’s systemic reactions. Among the other works cited in her journal: a biography about Young, and The Pale Horse by Agatha Christie.”