Life is infinitely stranger than anything which the mind of man could invent
—“A Case of Identity”
In the early Holmes stories, the detective’s use of scientific knowledge to bolster his investigations introduced the techniques of the laboratory to a mainly non-specialist readership. Moreover, in some cases, those techniques invented by Conan Doyle for his fictional sleuth would later inspire scientists and criminologists in the real world. For example, the French criminologist and medical doctor Edmond Locard greatly acknowledged the influence of the Holmes stories in producing his own laboratory examinations of trace evidence left at crime scenes. Locard produced articles related to the forensic analysis of cigar and cigarette ashes, dust traces, and handwriting throughout the early 20th century, all the while acknowledging Conan Doyle and his most famous literary creation.
“A Case of Identity” shows Holmes at his most inventive in terms of scientific analysis. In the March 1967 issue of the Journal of Criminal Law, Criminology and Police Science, David A. Crown noted the importance of the story to the later development of document analysis techniques used by police to investigate crimes and identify criminals. Crown stated:
The earliest known reference to the identification potential of typewriting, curiously enough, appears in "A Case of Identity", a Sherlock Holmes story by Sir Arthur Conan Doyle […] Doyle recorded in his diary that he finished writing "A Case of Identity" on April 10, 1891. The source of Doyle's data has not been ascertained, but it is of interest that his approach to typewriting identification is sound and that his terminology is precise. The earliest comment in writing by a document examiner on typewriting identification was…in 1894."
Writing in a 1970 issue of the same journal, Stanton O. Berg produced a wealth of evidence from the entire Holmes canon showing the influence of the great detective on forensic science techniques still used today. While there is no doubt that Conan Doyle utilized his own medical training and scientific education when writing the Holmes stories, he also showed a remarkable facility for predicting the type of scientific testing that would soon become commonplace in criminal investigations. As E.J. Wagner, author of the 2006 book The Science of Sherlock Holmes noted, “Sherlock Holmes may have been fictional, but what we learn from him is very real.” 120 years after the publication of “A Case of Identity,” the Holmes canon continues to inspire with its combination of literary fiction and scientific fact.