In "The Murder of Mary Russell," the character Lestrade inquires about the possibility of a knife being used and subsequently cleaned before being used to scrape blood off the floor. This question highlights the detective's focus on methodical investigation, rather than allowing preconceived notions to influence his conclusions. The dialogue conveys the importance of evidence in solving crimes and emphasizes a rational approach to hypothesis formation.

In the context of the murder investigation, the character's response underlines the necessity of relying on factual data to draw conclusions. By stating that he forms hypotheses based on evidence, he reinforces the scientific method's role in criminal investigations, showcasing the tension between intuition and empirical observation in detective work. This exchange illustrates the complexities involved in uncovering the truth behind a murder.