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Looking for motives in America's mass shootings

Kyle Knapp

Each time there is a mass shooting, discourse regarding motive immediately follows. Many assume that mental illness is to blame for extreme violence, which appears impulsive, amoral and irrational. We tend to think, “Someone who does this just has to be mentally ill,” indicating how we as a culture view the relationship between mental illness and violence. Providing adequate mental health treatment is an important issue, but the oversimplification of motive does not help in understanding why these events occur. It also contributes to the stigmatization of people with mental illness, who are more likely to be victims of violence than perpetrators. Motive is a far more complex concept.

I am a senior undergraduate student studying criminology at Hamline University.  For the past six months I have been helping Jillian Peterson, a forensic psychologist at Hamline University, and James Densley, a sociologist at Metropolitan State University, build a mass shooter database. Our research defines a mass shooting as an instance in which four or more individuals are killed in a public space with a gun in a 24-hour period. Shootings that occur in the process of other crimes, such as a robberies or gang activity, are discounted. Instances called “family annihilations,” where an individual kills other members of their family in rapid succession, are also excluded.

135 mass shooters in database

By this definition, there are 135 mass shooters included in the database over the past 60 years. They are coded on 50 different background traits that range from interest in past violence to social media use. I have been focused on understanding motive. In order to stop mass shootings, we have to understand what drives people to shoot in the first place. Although the project is not yet finished, my preliminary assessment of the motives of 135 mass shooters is that mental illness is not a common motivating factor.

After the shooting at Stoneman Douglas High School in Florida, the same national discussion about mental illness and violence began about Nikolas Cruz. The conversation first centered on his expulsion from the school as being the driver of his behavior. Then focus switched to depression that he experienced after the death of his mother.

These claims are possible explanations, but do not address motive. Cruz did not commit this school shooting because he was depressed, which is the normal response to losing one’s mother. His motive is far more complex than a diagnosis.

Path to violence: a slow build over time

Our work building the life histories of similar shooters has shown the path to violence is a slow build over time. These individuals do not just snap or experience symptoms of mental illness to the point of explosive violence. Stressors accumulate over time, coupled with a radicalization process that is then met with a trigger, usually in the form of a significant life event.

Currently, little is known about Cruz’s life or his motive. It seems that he expressed interest in past violence through social media postings. He took photos with guns, knives, and posted images of harm being done to animals. It is clear that more is going on than just depression.

He is likely an “injustice collector.” This behavior is defined by former FBI profiler Mary Ellen O'Toole as someone who neither forgives nor forgets perceived injustices. They do not cope with rejection or even minor setbacks and will sometimes express their frustration with violence. Elliot Rodger, the Isla Vista Shooter, is a prime example of one of these individuals. He was motivated by the urge to punish women for rejecting him. 

It is unclear at this time if Cruz has similar thought processes. Hopefully a clear picture of why he decided to commit mass violence with reveal itself in the coming weeks. The conversation can then shift to prevention strategies — specifically, the question of how to report, assess, and de-escalate threats of mass violence.

Kyle G. Knapp is a senior anthropology and criminology & criminal justice student at Hamline University. He has been a research assistant working on the Mass Violence Project since last September.


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Comments (17)

Our polarized society is too

Our polarized society is too much for people already in fragile states of mind. Forcing people to accept concepts that defy logic, science and tradition will invariably push some over the edge.

Bermuda Triangle fallacy

Studies like this may fall into something I call the Bermuda Triangle Fallacy. Sorry, I can't remember off hand what this fallacy is REALLY called, but BTF works so I'll use it.

Back in 1995 Larry Kusche published his investigation into the mystery of the Bermuda Triangle, it's an excellent book which I highly recommend :

Over a number of years Kusche went out and investigated each and every "disappearance" in the "Triangle" and discovered that the "mystery" of the Triangle simply dissolves once you discover that every disappearance has it's own explanation rather than a single explanation for every disappearance. Different things happened to every plane or ship that "disappeared" in the Triangle. Flight 19 got lost, ran out of fuel and ditched in the ocean. The Bermuda Triangle Mystery can only be sustained by the assumption that there must be a single cause for all of the disappearances, it'a bogus assumption.

Likewise, it's probably a mistake to assume that there is a discrete motive or profile for mass shooters. You can compile data, and there may be some similarities ( There are different types of planes and ships, but they're still planes and ships), but you're not going to find a comprehensive motive that describes all shooters.

I'm not saying this junk analysis or useless. This is social science, and social science will be social science, but ultimately the difference between a mass shooter and everyone else... is the shooting, not the profile. You can develop profiles but those profiles will not be unique to the American psyche, those same profiles will exist elsewhere. The difference will always be that whatever the profile, US shooters got their hands on guns and shot 4 or more people within 24 hours. Someone with a personality profile like this can sit around for a lifetime, and tens of thousands of them do... they don't become a mass shooter until they start shooting.

Social science is fine, but "understanding" shooters can't yield policy that will reduce those shootings, it can only tell us after the fact which profile shooters fit into. We have no instruments that can effectively predict violent behavior, the only reliable predictor is past violence and will remain so. The obvious conclusion will be that some people shouldn't get their hands on guns, especially assault weapons... I can tell you that right now without any data or profile.

Valuable work

This kind of research on all uses of firearms is essential to crafting good policy and uses resources wisely.

A working hypothesis...

Anger and vengeance, coupled with access to, and familiarity with guns.

(Psych professionals agree that "mental illness" seldom manifests itself in violent behavior.)

It's good to see someone

It's good to see someone doing research that does away with the broad and inexact "they're mentally ill" explanation for mass killings, to focus on individual cases and specific motivations. (The young man in Florida is perhaps too easy a case; try explaining what motivated the Las Vegas murderer--he seems to have disappeared from all media attention!)

Someone should begin research as well on the obvious gender issue: Why is it MEN who do all this mass killing?

And one cautions all the researchers: Never forget that these mass murders could not have taken place without semi-automatic or automatic firearms. The guns.

"And one cautions all the

"And one cautions all the researchers: Never forget that these mass murders could not have taken place without semi-automatic or automatic firearms. The guns."

That is something called a "pre-determined conclusion". It's the mark of every junk science practitioner out there.

It suggests that we ignore every incident that includes the use of feet, fists, hammers, knives or any other weapon that accounts for the *overwhelming majority* of violent deaths in America.

Science is actually a real thing

A predetermined conclusion is one that is established in advance without data. The observation that someone who shoots people could not shoot people without a device that shoots people is simply a logical truism. Beyond that we have decades of data, reliable observations, and experience with gun violence that lead to the conclusion widespread availability of guns, and certain types of guns, is responsible for our gun violence. This is not a predetermined conclusions, it's a conclusion based on decades of reliable observation. Meanwhile one should understand the difference between: "denial" and skepticism if one is going to dabble in "science".

If you're going to apply

If you're going to apply science to the question of why some people commit mass murder, and you focus on one method to the exclusion of all others, you're engaging in junk science for use in political propaganda. It's a case study in why Congress won't fund junk science.

That's mass murder, by the authors own definition. There are hundreds of murders committed with hammers every year. We need to get to the bottom of this.

Again, science is real thing

If you're going to claim that people with hammers commit hundreds of mass murders every year, you need to present some reliable observations to support that claim. Scientific method does not allow claims that aren't supported by reliable observations.

In the meantime I'll point out again that it's always the gun experts in the room who suddenly can't tell the difference between banjos, hammers, and assault rifles whenever we have conversation about gun violence.

You're not doing science, your debate gaming. Obviously mass murders are committed with weapons other than guns, but the majority of mass murders in the US are committed with guns. The US is the only country in the world that even has a statistic for toddler gun killings, and it's obviously ridiculous to claim that the Las Vegas killer could have accomplished same level of devastation armed with hammer instead of an assault rifle. Why do we spend so much money arming our soldiers with assault rifles when all they really need is a good hammer?

Another thing about science that a person might want to understand is the nature of scientific discussion. It's important to understand the research being done and the claims being made. Thus far no scientific investigation has or is likely to claim that the mere existence of guns creates school shootings. Rather the data simply indicates that ability to obtain guns equips people who engage in school shootings and other mass murders like the one in Las Vegas. The acquisition of that weaponry makes it possible to kill and injure large numbers of people. Logically if these attackers had not been equipped with assault weapons, they would not have able to kill so many people. This is why countries where people cannot easily obtain such weapons have few if any attacks like the ones we routinely see in the US.

Debate games are not science, they're sport. A scientist would have noticed that this article does not in fact focus on proving that guns are responsible for massacres in the US, on the contrary it focuses on the psychological profile of those who commit these awful attacks. It's the debate gamer who's arguing that guns have nothing to do with gun violence that's being unscientific... but since debate gaming isn't science we don't expect it to be scientific do we?

On the Right Path

This study is a start towards an understanding of the path to mass murdering and other Anti-Social behaviors. Once we see the steps we can look for resilience factors that prevent most from taking the final shot.
Yes there is a Bermuda Fallacy, but it is not assuming commonality to the shootings. It is that one event is the answer. Just like the School to Prison Pipeline there is a path to mass shootings.

God in Schools

The motive no one wants to admit is how we've taken God out of the schools and the effect that's had on the children of our society.

In the 1950s in junior and senior high school, we brought our rifles to school and put them in our lockers for the day. We even had firearm safety training right at school. There were no mass shootings back then. These were the days before the "separation of church and state," before the pledge of allegiance and prayer in schools had been attacked as now happens so often. Our founding fathers considered this a Christian nation, but today we have a MN congressman who swore his oath on the Koran.

As John Quincy Adams said, "There are three points of doctrine the belief of which forms the foundation of all morality. The first is the existence of God; the second is the immortality of the human soul; and the third is a future state of rewards and punishments. Suppose it possible for a man to disbelieve either of these three articles of faith and that man will have no conscience, he will have no other law than that of the tiger or the shark."

Religion is certianly a

Religion is certianly a stabilizing influence in many families, but it's not the only path.

Sports, music, art, hunting, car projects, are all things that bring parents and kids to spend time together and at the end of the day, that's what attention to your kids.

The one thing these disturbed kids share is isolation. Society, and their families ignore them. In Cruz's case, even law enforcement ignored him.

Pay attention to your kids.

Do you think?

Religion could also be a destabilizing force?


What a weak and impotent God one must believe in to claim that he/she can be taken "out" of schools by a mere court ruling? I had no idea Judges were so powerful? If we can erect impermeable anti-God shields around our schools with mere court rulings why are we worried about protecting ourselves from N. Korean missiles?


So God is upset and is allowing mass shootings to take place as a punishment? Or are you implying that the only reason a person should be good is for fear of eternal damnation? As for your assertion that all this took place before "separation of church and state" and the horror of having a Muslim congressman, the first amendment prohibits congress from promoting one religion over another and Article Six of the Constitution states that no religious test shall be held for holding a position in the US Government.

First of all, you must

First of all, you must believe in a very puny God if you believe in one who can be kept out of any human building.

Second, you have to explain the fact that countries that are much more secularized than the U.S.--and the U.S. is the most religious of the Western industrialized nations--have few or no school shootings.

Third, students are allowed to pray in school. It's just that no teacher or other school employee can lead them in prayer, but student-led prayer is fine. Remember the kid in Arkansas who in 1998 shot a group of fellow students who gathered every morning outside the school to pray?

By the way, school prayer was never a nationwide phenomenon. I was in sixth grade in Wisconsin when the 1962 Supreme Court decision banning compulsory school prayer and Bible reading was handed down, and my classmates and I were puzzled. There were places where people had to pray in school?

When the Republicans began agitating about school prayer in the early 1980s, just when there when the first young parents who didn't remember 1962 were coming along, I polled my older relatives and my friends from graduate school. Neither of my parents, one from Minneapolis and the other from a small town up north, had ever had school prayer. My maternal grandmother, born in 1899, had never had school prayer. None of my Midwestern or West Coast friends had ever experienced school prayer.

My friends from the Northeast and the Deep South had, and after all, the Supreme Court decisions were about laws from New York and Pennsylvania, which were established in a panic about Catholic and Jewish immigrants "overwhelming" the Protestant majority. (One reason for the nationwide existence of Catholic schools is that the public schools in the late nineteenth and early twentieth centuries could be hostile environments for Catholic students.)

As far as the Deep South is concerned, it's a place where the religious spectrum runs all the way from Methodist to Baptist to Pentecostal, and there are still isolated reports of teachers or schools who create a hostile environment for non-evangelical students.

I wonder how school prayer advocates, most of whom are evangelical Protestants, would feel if they were transferred to Hawaii and ended up in a public school where most students were Buddhists. Would they be happy with a hypothetical state requirement to start each day with "Hail to the Jewel in the Lotus"? Or in the more likely event of moving to a heavily Catholic city, would they be fine with having their children say the Rosary each day?

What I'm getting at is that most of the country never had school prayer and rarely had school shootings.


We've always had violence in the schools, and there was gun violence shootings. The mass shootings that emerged beginning in the mid sixties are a product of increased civilian ownership of assault weapons. I've actually graphed this out:

Guns are dangerous and training doesn't make them safe. Every year thousands of "trained" American's accidentally, and deliberately shoot themselves and others. This is why firearms are so tightly regulated on military bases despite extensive training and familiarity. Mass shooters are not unfamiliar or uncomfortable with their weapons, on the contrary. Nor are massacres accidental events committed by people who weren't raised in an appropriate gun culture.