In 1842 the first detective department was starter at Scotland Yard. It had only two inspectors and six sergeants. Detectives did not wear uniforms and they investigated more complicated crimes. In 1878 the detective department (CID). Mr Gregon in ‘The Red Circle’ worked for this department.
In ‘The Red Circle’ Mr Leverton worked for the Pinkerton Detective Agency in the United States. This agency was created by Allan Pinkerton in Chicago in 1850 and today it is the oldest in America. Allan Pinkerton became famous when he discovered a plan to kill president-elect Abraham Lincoln. During the American Civil War President Lincoln used Pinkerton Detective to protect himself and his family.
Sometimes detectives did not do a good job and made a lot of mistakes. Other times it took them months to solve a case. And at times they never solved the case. Some people paid private detectives (like the character of Sherlock Holmes) to solve difficult cases.
In Conan Doyle’s stories Sherlock Holmes solved cases with modern scientific methods called forensic methods. He used chemical analysis, microscopes, fingerprints, photographs, studies of handwritting and footprints. In real life detectives did not use these methods yet. In 1901 Scotland Yard starter using fingerprints to solve cases.