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Why do people kill?
That’s a question a lot of thriller and mystery writers ask themselves when they’re plotting a new story.
I apologize that this is more grim than my usual posts, but writers, we sometimes deal with things like this! This post is kind of a mini murder motive generator for writers, and if you like it, you’ll also want to check out my 25 Mystery Clues for Writers.
Let’s get into it!
1. A physical fight turns deadly.
When we’re asking, Why do people kill—or what makes a human being cross that line—it’s important for mystery writers to remember that sometimes it’s accidental. A murderer may inflict more damage than they intended. On the other hand, it’s also possible that in a fight, the murderer becomes enraged and decides to kill the other person instead of just hurting them.
2. Someone murders their spouse, partner, or ex out of jealousy.
In the U.S., men murder about seven times more often than women do. The majority of female murder victims are murdered by a husband, boyfriend, or a male ex, and jealousy is one of the main motives in these cases. Risk factors here include a male partner who is abusive, who uses alcohol, and who owns a gun. Of course, women may murder out of jealousy, too.
3. The murderer hates the victim’s politics, religion, or sexual orientation.
In a case like this, the murderer may feel like a crusader.
4. Someone murders an abusive partner or family member because they’re sick of the abuse.
The abuse may be physical or emotional.
5. The murderer kills the victim in order to steal from them.
This may be premeditated murder, or it may just happen in the course of a robbery.
6. The murderer wants to collect life insurance money or an inheritance from the victim.
This is a really popular reason that a character becomes a murder suspect in a murder mystery novel.
7. A spouse wants out of a marriage, but doesn’t want to pay alimony or have others think badly of them.
In this case, the murderer views murder as a means of “instant divorce.”
8. The killer wants to eliminate a rival.
This could be a rival in love, politics, or some other type of competition.
9. The killer is taking revenge for being wronged in their career.
The victim may be a boss who fired them or a business partner who cheated them.
10. The murderer is taking revenge for a loved one who was wronged.
For example, this could be a father killing his daughter’s rapist, a son killing the man who ruined his father financially, or a mother killing the bully who drove her son to suicide. Of all the answers to the question Why do people kill, this is probably the easiest one to understand.
11. Someone takes revenge on a person for rejecting their romantic overtures.
While the murderer in this case has not been wronged, they may still perceive themselves as being wronged or humiliated.
12. Some mistakes the victim for their actual intended victim.
After I wrote this, I remembered that I have firsthand experience with it! I lived in a duplex and there were gunshots one night. It turned out that my neighbor had a friend staying with her, and the friend’s ex-boyfriend came by with a gun. When my neighbor came to the door, he shot at her from his car, believing her to be his ex-girlfriend. He just missed—the bullet hit the doorframe. I’d been outside just minutes before, taking my trash out to the curb.
13. Someone murders a family member that they perceive as needing an extraordinary amount of caretaking.
This is a very sad situation, and it does happen.
14. Someone murders their pregnant partner due to extra stress and/or fear of responsibility.
In the U.S., people who are pregnant are much more likely to be murdered by their partner than to die of any other pregnancy-related cause. One option here is that the murderer is a married man whose mistress has gotten pregnant.
15. The victim was a witness to a crime.
This is definitely one to consider if you’re writing a thriller or mystery!
I hope this list was helpful for you! I have more motives for murder in my book Master Lists for Writers. Check it out, if you haven’t already!
Writers, any other answers to the question, Why do people kill?
If you have other ideas, or general thoughts about writing a great murder mystery plot or subplot, let me know in the comments! Thanks so much for reading, and happy writing!
fantastic list
(PS. I think gender identity is the preferred term over sexual orientation.)
denise
Oh you know what, I’m no expert, but we might be talking about two different things there. Sexual orientation = who you are sexually attracted to (gay, straight, bi, etc.), and gender identity = what gender you identify as. But gender identity can be a reason for prejudice and hate, too, so I could’ve added it to the list!
Another wonderful and insightful blog. I am writing a Romantic Suspense story.
Alex became a bodyguard to a mobster when he saved his life. The man offered him a job as a bodyguard because he needed the money he accepted, thinking it would be for a short period. The mobster was killed one evening. Alex killed the killer of his friend(the mobster.) He saw this as an opportunity to get out of the mob. He killed to protect someone.
Zenia killed two people. Her husband was a mobster. One night, he went down to the kitchen to warm a bottle and feed it to their baby. Someone broke in and when they shot him in the back, they killed the baby too. Grief stricken and in rage, she killed two people who were with the true murderer.
Theme: Sometimes good people do awful things.
Thanks for the kind words, Carol! It sounds like you are really thinking through motives in your story. I hope the writing is going well! Thanks for commenting!
Someone murders someone who they know will continue harming innocent people if not stopped and the justice system has failed to stop them.
Bill, this is such a good one! Thanks for suggesting it!
Is this a good defense? Like “stand your ground” law/defense
Good morning Bryn
May I add a motive ?
The killer has murdered someone who was the witness of a financial fraud
Thank you for your blog I like to read it !
Hi, Philippe! Oh, that’s a really good suggestion for a motive. Thank you! And thanks for reading, and the kind words. 🙂 Have a great weekend!
Then there’s the psychopath/sociopath – no motive required 🙂
That’s true!
True
This one kind of goes along with #10:The murderer is taking revenge for a loved one who was wronged…
Someone was blamed for a murder and being attacked my the victims loved ones, the person in love with the accused murders all the people who attacked the accused person. But then what if they confess their undying love for that person and they don’t reciprocate those feelings so they kill them too?
This is an intriguing topic, yet I am amazed while reading this. Honestly, I do not know how to express my thoughts, but all I know is all people are born good people, and if we choose to love rather than hate, maybe crime will be lessened.
Whatever the motives is, killing someone is not a solution.
This one is not in your list, so I guess it is not as common as I thought. Ex-wife kills former husband (revenge) and his new wife (jealousy). In this case, she doesn’t pull the trigger personally, she encourages her brother to go after them, not only for wronging his sister, but plays upon her brother’s paranoia and desire to eliminate a perceived rival, the new wife’s illegitimate oldest son. The son was the only one of the three actually murdered, the other two committed suicide.
This is a true story — it all went down in 30 BC. But there is no documentation that the ex-wife (Octavia) had anything to do with the Roman senate, after years of propaganda issued by her brother (Julius Caesar’s heir), Octavian, declaring war against Egypt and her former husband’s new wife, Cleopatra. To this day, the two suicides and the murder of Julius Caesar’s teenaged son is attributed to collateral damage from the defeat of Egypt in the war, although historians admit that Octavian, adopted posthumously by Julius Caesar (after he had been assassinated), feared that his claim to the throne might be threatened if Caesarion ever showed up in Rome with that intent.
History only records that Octavia moved back to Rome with her and Mark Antony’s children three years after they had been abandoned by Antony in their mansion in Athens.
Conversations between Octavia and her brother after she moved back to Rome are strictly speculation on my part. I came to your website seeking confirmation that, upon occasion, ex-wives have been documented to have caused the death of a husband’s new lover.
I just reread your list, and I see that the death of Cleopatra (induced suicide) IS on your list. Twice, in fact. Number 8 is that the killer wants to eliminate a rival. It appears that Octavia wanted her husband and father of two of her children to come back home, so might have been motivated to cause the death of her husband’s new wife, Cleopatra. Number 10 is “The murderer is taking revenge for a loved one who was wronged.”
Octavian loves his sister, knowing that she was a faithful wife, and might be motivated to cause the death of the person (Cleopatra) who is guilty of stealing his sister’s husband and breaking his sister’s heart. However, we know that Octavian did not want Cleopatra dead. He wanted to strip her wealth, and take her captive to Rome, and march her in his triumph (victory parade).
He was in the process of doing that when she committed suicide.
One thing is for sure. Mark Antony was in a very dangerous situation — being in a love triangle with the two most powerful woman on earth. He should have dumped Cleopatra and gone back to his wife before the war started
You started off with why people kill people and then focused upon murder.
So if killing only:
What about as a soldier?
Or self defense?
Or unintended (e.g.’ driving intixucated)?
What if someone was mentally ill? I’m not talking about someone who can’t control their urges to hurt people, or is crazy, I’m talking about someone who felt like they were slowly going insane. At first it felt like they were dying, crumbling piece by piece, until they realized that they weren’t dying, they were changing. More manipulative, more emotionless, yet they fell too much all at once. And the only way they could deal with this was pain. It started simple, just a scratch. A scratch became more, more lines, more common, the morning the scratches scabbed over. Then knives scraped along skin, not deep enough to leave a mark, they couldn’t know, but deep enough that it was enough. And it helped, it did. They said it was a distraction, something to draw their mind away from the thoughts, the feelings, the emotions, nothing more. But soon, they craved it. Like it was a drug. They wanted to see the scarlet drip from their arm as they scratched, pour from their side if they stabbed. If. But they couldn’t, whether it was from fear or something else, they did not know. But they wanted pain. If it was theirs… or not. They thought about how easy it would be to kill their parents, medicine in their mother’s cup, a hammer to father’s head while he slept, how easy it would be. Even though their parents had apologized, part of them never moved on. They say they regret it. But it always felt fake to the child. Yet when faced with the simplicity of their parent’s death, they didn’t. They could have laid the evidence right next to her, as if she had committed suicide, but they could not do it, for no matter how their mother treated them in the past, her and the father loved their child with all the love they could and they loved their parents as well, not knowing what to do without their guardians in their life. But their thirst for pain, blood, even death, continued without prevailing. And now they were lost, in their thoughts, in their life, while feeling like they were slowly being driven mad, with no clue for the next steps. Would they be better off dead? Although they felt like everyone would be happier if they were gone, and they didn’t exactly want to become a killer, they didn’t know if they were ready to go just yet. Besides, they were still young, only a young teenager. But everybody is a killer when you push them far enough, or simply when they can’t stand it anymore.
Hey there. Since this website is mostly about writing, I am guessing this is a creative writing exercise. If it is, it’s very well-written. But if you are harming yourself or struggling with the urges to harm yourself or others, I hope you will talk to a licensed mental health professional as soon as you can. I know it can be difficult to ask for help, but thoughts like these aren’t as uncommon as you might think, and with treatment, they can be overcome so that you can live a more balanced life with more peace of mind. Again, if this isn’t your real experience and this is fictional writing, you did a great job.
Thank you for your kind words, I had just gotten caught up in my writing, I apologize, but this is not from my life experience. My close friend had actually described their suffering as so not too long ago, but now they are getting help and are better than they ever were. I simply wrote this since I was curious if you had an opinion on this situation overall, but I ended up getting distracted when it came to detail. I was possibly considering the idea of writing a novel based on what they had gone through, as I had already gotten their permission, but I don’t know if I should focus on a different topic. Any ideas or suggestions from you would be greatly appreciated.
Hey, thanks for getting back to me! I am glad your friend is getting help and doing better. Someone told me once about dark thoughts that they are like the lowest keys on a piano. They’re there, but you don’t have to keep banging on them if you don’t want to—you can focus your mind to lighter melodies. That helped me before with depression, and it might help with other dark thoughts, too. Being active and taking walks, and enjoying books, movies, and TV that are more uplifting, are things that helped me, too!
My caution with writing a book on those experiences is that it will mean that you, as an author, will have to spend a lot of time in that dark space, and you might not want to do that. It is really up to you. Another option is to write about a character who has recovered or is recovering from that kind of mental health space.
Thanks for reading the blog. I hope you have a wonderful 2026!
Thank you for your opinion, I will take that into consideration, but I am prepared to have to deal with those thoughts as well, if necessary. I wish you a happy New Year as well!