If we’re honest with ourselves most – if not all – of us had one moment in our lives where we were so enraged we fantasized about taking the life of another. Maybe it was a protective mother on a playground with her three year old during an attempted abduction. Maybe it was a husband in court listening to graphic testimony by the medical examiner about the homicide of his wife, while the defendant sat in front looking bored.
The good news is, the far majority of us brake a homicidal impulse early in situations where it is not “do or die.” We cannot cross the Rubicon. Our inner controls won’t let us. (Not unless our life – or the life of a close vulnerable person – is actually on the line.)
That said, in the U.S. today about 20,000 known murders do occur annually. However, there has been a gradual overall decline in homicide since 1990.
(The huge jump in 2019 was historically unusual. Homicides rose dramatically during COVID. Experts attributed this to supply disruptions, social instability, economic strain, isolation, gun purchasing spikes, and breakdowns in normal routines.)
Since COVID-19, murder has dropped at one of the fastest rates seen in decades. The FBI reported an 11%+ drop from 2022→2023 and another major decline in 2024.
(Public perception still lags behind reality. Many Americans mistakenly believe homicide is continually rising even while national rates are falling. The “everything is more dangerous now” narrative is psychologically driven, not data-driven. This is due to the 24-hour news cycle, social media repetition, politicians, and true-crime saturation in podcasts, movies and books.)
Who Kills?
Ask the average person to imagine a murderer and they are likely to describe a shadowy predator lurking in a parking garage, an entitled serial killer stalking strangers, or an enraged teenager walking into a crowded school with a large, loaded weapon.
The image is cinematic.
It is emotionally gripping.
And statistically, it’s uncommon.
So what about those among us who do kill?
Most deaths are not committed by heartless “monsters” in the cinematic sense. They emerge from:
- dysregulated nervous systems,
- humiliation,
- rage,
- intoxication,
- trauma,
- impulsivity,
- desperation,
- entitlement,
- attachment disturbance,
- or chronic threat perception.
And typically within our own social or vocational circle.
Most murderers are not masterminds. If they were our prisons would not be housing so many. Instead, they are dysregulated human beings whose nervous systems, thinking patterns, impulse control, and emotional regulation have deteriorated under stress, substance abuse, grievance, entitlement, or chronic threat perception.
But let’s focus on the physiology of murder. What goes on in the brains of killers?
The Physiology of Homicidal Behavior
Homicide is often less “evil genius” and more “overheated nervous system plus catastrophic cognition.”
For purposes of this blog entry I am going to set aside the estimated ten per cent of people (worldwide) who are psychopathic predators. Their brains are literally different from the masses from birth. They are cool under fire, escape notoriety if possible and have no regrets about their actions – if they even give them much thought at all. These are the hired assassins, cartel leaders, serial murderers and some with a manifesto. And, thankfully, they are uncommon.
Instead I want to focus upon the other 90%. These are the majority of killers. I will approach this sequentially.
Before the Homicide:
In the months or weeks leading up to taking another human life, “threat detection” in the brain triggers a dangerous shift away from reflective thinking and thoughtful decision making, to survival mode. The future killer often rehearses lethal scenarios long before it actually occurs. This simulation activates many of the same brain networks involved in real lethal acts.
In other words, while it may look impulsive to the outside, homicide more often develops progressively. An interruption at that point may de-escalate the outcome. When imagining the murder itself, the same neural pathways involved in a real murder “light up.”
Their poor reasoning may account for why many consult the internet for information ahead of time on how to dispose of evidence, build weapons, intimidate witnesses, compute toxic doses, stalk someone, or how to evade police. It’s not surprising when you think about it. A.I. is just replacing more conventional methods distressed people used to gather the same information, such as discussions with a close friend, bartender, talk radio or a posting on anonymous message boards.
The person who will murder is often under chronic stress. They may have unresolved tragedies from their past. They frequently fear humiliation, disrespect, failure, homelessness, joblessness or abandonment. There is a good chance they’re under the influence of drugs or alcohol while rehearsing this behavior (but this is not universal).
And over time certain brain regions, especially the amygdala (the brain’s alarm center) and the prefrontal cortex (an area responsible for judgment, anticipation of consequences and regulation of emotion) deregulates.
The combined result? The brain of the future murderer becomes less capable of resisting impulses and rational thinking. This, in turn, moves the needle beyond homicidal thinking to homicidal action.
Then comes the triggering event.
It could be an accusation, a rejection, being fired, feeling publicly humiliated, fear of exposure, intoxicated conflict, partner infidelity, strained finances or the belief that one is being cornered emotionally, financially or legally. It is a perfect storm brewing.
During the Homicide:
The triggering event is a catastrophe waiting to happen. During the toll of negative emotional arousal, the brain undergoes rapid and lethal change. The heart rate accelerates. Adrenaline surges. Pupils dilate. Fine reasoning declines. Attention narrows. Tunnel vision develops. Even hearing narrows down to what is immediately in front of them. Thinking becomes fragmented and many report feeling “robotic like.”
This is not a calm decision. It is not an impersonal act. Everything boils down to eliminating the “danger” in front of them. The triggering event is a trip wire, a flip of a switch, a tipping point.
Many report feeling “outside their body” or “blanking out.” This may be true. It may be manipulation. Either way it does not excuse it.
After the Homicide:
After the murder, time abruptly stops. The surge of brain misfirings declines and the physiology of the brain shifts again. Specifically, adrenaline drops quickly. Cortisol (a stress hormone) remains elevated. Shock emerges.
And what of the prefrontal cortex under the forehead? This is the thinking brain that comes back online imperfectly. It is experienced as the “Oh shit! What have I done?!” moment. Reality looms large. Decisions must be made in spite of the skewed brain functioning. So, some perpetrators may flee, vomit, set the crime scene afire, panic or sink in an eerie calm. Some may call 911, or sit beside the body for hours as they absorb their new reality. A subset takes their own life and others will search online to figure out their next move.
This is a re-entry phase. Logic is returning but is fragmented. Thinking is more in the immediate time space, not long term. Attempts to reconstruct what happened is prone to error and memory gaps as time goes on.
After the initial panic of realization exhaustion follows. An eerie calm is not unusual. It is sometimes misinterpreted as lack of remorse. But acute shock “flattens” emotions
It is not unusual for the slayer to replay the events in their mind over and over. That does not mean their recall is accurate, but they ruminate about what happened. And when they do, it is not unusual to experience symptoms of trauma themselves – the hypervigilance, insomnia, intrusive images, startle response, confusion, speech errors, and so forth.
While this does not replace culpability, it does remind us that we as a species are wired not to kill. So when we do, it comes at a price.
Recap
Most reactive violence does not emerge in a vacuum. It resembles earthquakes. Long before the visible rupture, pressure has been accumulating silently beneath the surface — stress, grievance, trauma, humiliation, fear, addiction, jealousy, sleep deprivation, dysregulation. The final trigger may appear small to outsiders, but it strikes an already unstable fault line.
The actual homicide may last minutes. But the nervous system story behind it begins many months to years earlier. Punishment starts after the rupture and so does the grief of survivors who will carry it to their grave.
