In defense of Conan Doyle, Wikipedia says:

Sherlock Holmes remains a great inspiration for forensic science, especially for the way his acute study of a crime scene yields small clues as to the precise sequence of events... All of the techniques advocated by Holmes would later become reality, but were generally in their infancy at the time Conan Doyle was writing.

and goes off to claim that later detective fiction actually became less realistic as writers shifted attention to psychology rather than forensics.