For criminals in the twentieth century, cleaning up a scene to erase fingerprints or wearing gloves while committing a crime was basic common sense, because fingerprints could serve as evidence.
But in the early nineteenth century, fingerprints could not be used as evidence. It was not until the mid-to-late nineteenth century that people realized everyone's fingerprints were different.
Social demand was the fundamental driving force behind the development of evidence science. But evidence science did not refer to forensic techniques such as fingerprint imaging, DNA testing, or bloodstain identification. Rather, it was a state of interdisciplinary research between evidence law and other fields. Take a medium's testimony, for example. Eyewitness testimony was not much more accurate than theirs. Many factors could affect an eyewitness's memory, such as lighting, disguises, and the rate at which memories faded. When eyewitnesses were asked to identify a suspect from a lineup, they might not even be able to tell them apart at all.
When a case occurred, people focused on different things. Some noticed the knife first, while others noticed what the criminal was wearing. Change the clothes, and the eyewitness no longer recognized them—unless they had received specialized training in identifying physical features. Those who needed such training for their everyday work were usually police officers and detectives. That was why John Fielding encouraged people to report crimes as quickly as possible, to provide as much testimony and as many clues as they could while their memories remained clear. Sometimes he even hired artists to draw portraits of criminals based on victims' descriptions and print them on wanted posters.
But this also brought an undesirable consequence: perjury. Especially after the reward system was introduced, it caused a great many problems with false testimony. At the beginning of the eighteenth century, lawyers were not