One of the great things about writing murder mysteries is the opportunity to imagine the mind of the villain. After all, no matter how many times we say we’d like to kill someone in real life, most of us thankfully aren’t ever going to get closer to the mindset of an actual murderer than that. So creating a realistic culprit is a true exercise in imagination, and it almost always involves the reason why the killer did it. Your villain’s motive can be a crucial element of your mystery, and it can even help develop the rest of your book’s plot.
In real-world murder investigations, motive is almost always a key question. The victim’s relationships are searched for enemies, and the initial suspect list is frequently populated by people who had a reason to commit the act.
In murder mysteries, the revelation that a character wished harm on the victim can provide a strong clue to the reader—unless, of course, many other characters had a reason for the murder as well. In stories where no apparent motive is provided, it’s still important—even after the killer has been identified—to give a believable explanation for why the culprit did it.
On the lists of reasons why people commit murder, strong emotions like love or hatred hold prominent spots. That’s not surprising, as most people require an overwhelming impetus to do something this extreme. After all, love and hatred have been the prime motivations in tragic literary tales since time immemorial. Unfortunately, an intelligent killer would probably know that a strong attachment (or aversion) to the victim could place him or her on the suspect list if that feeling isn’t a secret. This might not stop the murderer, but it could force an adjustment in the plan: A killer whose strong feelings toward the victim are well known might deflect suspicion by making the death look like an accident or suicide, or by building a believable alibi.
This might not be necessary, of course, if the strong emotions which prompt the killing aren’t directed at the victim. If Character X loves Character Y and feels Character Z is mean to Character Y, X’s love of Y could lead X to kill Z—and if there’s no evidence connecting X to Z, the love motive in this murder might not be obvious at all.
For mystery writers, this might open a broader avenue of consideration when plotting the story: In the case of a murder involving concealed motives, an intricate web can be spun around who knows what about whom. In the prior example, if Y knows about X’s feelings (or learns of them after Z is killed), Y just might go to the police. However, if Y returns X’s affection, Y might lie to protect X instead. If someone else knows about X’s feelings for Y and connects that with Z’s perceived mistreatment of Y, that individual could blackmail X, or even Y, and perhaps provide X or Y (or both of them) with a new motive to kill.
This nicely leads to the issue of perception in a murderer’s motivation. The initial investigation into possible motives frequently involves the question, “Did the victim have any enemies?” The results of those inquiries could be based in fact (X once threatened Z in public) or they might be mere suspicion (an unsubstantiated feeling that X disliked Z). Interestingly, perception can also be a motive for a story’s culprit—and the more ambiguous the motivation is, the harder it will be for the investigator to find. A perceived insult can elicit deep resentment even when no insult was intended. An imaginary rivalry can lead to unexpressed feelings of loss and humiliation. The impression of being unappreciated or ignored can spur a character to take drastic action. If any of these motivations exists only in the mind of the killer, the victim will have little or no warning and the investigator may be left with no suspect.
A similar scenario involves the killer who hides the feelings or circumstances which prompt him or her to act. Knowing that a murder investigation will involve the hunt for motive, the culprit may go to great lengths to appear friendly with the victim. Motives beyond the emotional can factor into this part of the discussion as well; a killer who has no feelings for a victim who is simply “in the way” might try to conceal the benefit they accrue from the victim’s removal. To revisit the XYZ example, if Y and Z were dating each other and X killed Z in order to date Y, X might wait quite some time (or start a relationship with someone else) in order to hide the attraction to Y and the benefit of killing Z.
Motive is a key element in most murder investigations, and it’s an excellent starting point for plotting a murder mystery. As we’ve seen from these few paragraphs, it can also help develop the rest of the story by suggesting ways the killer could cover his or her tracks, pointing the investigation in a certain direction, causing other characters to lie or make dangerous demands, or demonstrating that the reason for the murder might be apparent only to the killer. Sounds like one heck of a mystery—at least in my book.