"Murderers will try to recall the sequence of events, they will remember exactly what they did just before and just after. But they can never remember the actual moment of killing. This is why they will always leave a clue"

This quote by Peter Ackroyd recommends that killers frequently have difficulty keeping in mind the specific minute of killing. They might be able to recall the sequence of occasions leading up to and following the murder, however the real minute of killing is often a blur. This is why murderers frequently leave hints behind, as they are unable to keep in mind the details of the criminal activity. This quote implies that killers are not always able to keep in mind the details of their crime, which this can be used to identify them. It likewise suggests that the act of killing is so traumatic that it is tough to bear in mind, and that this can be utilized to the advantage of law enforcement. This quote is a pointer that even though killers may try to cover their tracks, they typically leave ideas behind that can be used to identify them.