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Tracking mass shooting events back through the decades is a difficult and incomplete task

And there's a surprisingly difficult question: What exactly is a mass shooting?

CNN  — 

The headlines are hard to miss: The Las Vegas massacre, in which at least 58 people lost their lives, is the deadliest mass shooting in modern US history.

Why “modern” history, though? Doesn’t it seem like an odd distinction to make?

There are a few reasons why you’re seeing that phrase. It has to do with how long we have been keeping track of gun violence statistics, how “mass shooting” is defined, and how we tend to regard past mass killings in our history.

The data just isn’t there

One of the biggest reasons, from a perspective of accuracy, is that tracking mass shooting events back through the decades is a difficult and incomplete task.

James Alan Fox is a criminologist and author who has been studying mass killings since the 1980s. He says there’s no official data that can be traced back through our country’s history, and modern databases must collect their information ex post facto, which makes for more room for missed incidents the farther back in time you go,

“That’s the problem with active-shooter data when you try to go back several decades,” he tells CNN. “It’s a matter of ability to recover cases. Lots of newspapers weren’t digitized, news archives aren’t always maintained. There’s no historical data.”

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Most reliable non-government mass shooting resources were started after notable mass shootings. The highly-cited Mass Shooting Tracker from the Gun Violence Archive was started after the Sandy Hook massacre in 2012 and has only tracked data since that point. Mother Jones started its mass shooting investigation after the movie theater shooting in Aurora, Colorado, also in 2012. Their data tracks back to 1982.

As for government reports, Fox says he looks to the FBI’s Supplementary Homicide Report, which was first issued in 1968 and was changed drastically in 1976, with added variables and connection allowing for better research and tracking.

The definition isn’t there

Reliably quantifying mass shootings requires answering a surprisingly difficult question: What exactly is a mass shooting?

The FBI has traditionally considered mass shooting any incident in which four or more people were killed during a related event, but in 2013 a congressional act defined “mass killing” as “three of more killings in a single incident,” and labeled mass shooting as a type of mass killing.

Additionally, some authorities like the Congressional Research Service add different provisions, which can eliminate gang-related activity, robberies, home invasions and domestic incidents from the figures.

Independent resources often use their own definitions. For instance, the Gun Violence Archive defines a mass shooting as “four more more shot and/or killed in a single event … at the same general time and location not including the shooter.”

These varying definitions not only make it more difficult to analyze past data, Fox says they also make it difficult to convey an accurate picture to the public on how often mass shootings actually occur and what their nature is.

“When you include wounded and dead in the same figure, it conflates two different things: How many victims and what happened to them,” Fox says. “Those numbers are always in the wake of a mass killing, where people tend to focus on the dead. And when you have statistics based not only on the dead, it’s representing a different type of incident than people are focusing on at the time, and its making those numbers look like they mean something they don’t.”

Two points in time changed the conversation

While mass shootings have always been a part of US history, some of them far deadlier than any incident covered on a TV or newspaper, the real era of what we culturally consider to be a “mass shooting” started in 1949.

On September 6 of that year, Howard Unruh strolled through the streets of Camden, New Jersey, and killed 13 people with a German Luger pistol. To many historians and experts – Fox included – the unemployed World War II veteran’s so-called “walk of death” was the first time in modern history the country was confronted with the typical mass shooter profile: An angry, anti-social loner shooting and killing indiscriminately.

There was another reason Unruh’s rampage was such a pivotal event.

“There have been notorious killers since America was founded, but you didn’t have the mass shooting phenomenon before Unruh’s time because people didn’t have access to semi-automatic weaponry,” true crime novelist Harold Schechter told the Smithsonian Magazine in 2015.

In Camden, New Jersey, on September 5, 1949, Howard Unruh, a World War II veteran, shot and killed 13 of his neighbors. After barricading himself inside his house, police overpowered him a day after the shooting. After a number of tests were conducted, he was ruled criminally insane and was committed to a state mental institution.

The second moment that changed the conversation wasn’t a moment, but a year. In 2012, the country endured two high-profile mass shooting incidents in short succession: On July 20, 12 people were shot and killed in a movie theater in Aurora, Colorado. On December 14, 20 children and six adults at the Sandy Hook School in Newtown, Connecticut. The assailant, Adam Lanza, also killed his mother before the massacre.

It is no coincidence that this dark time spawned an awareness and desire for more specific gun violence information, like the mass shooting resources discussed previously.

“2012 was a really big point where people started paying attention,” Fox says. That was also the year that mass shootings were voted the top news story of the year in the AP’s annual poll.

“The conversation used to be about serial murderers,” Fox says. “There were school shootings and workplace violence, but there wasn’t a lot of interest in the phrase or subject of mass killings until 2012, which saw a huge rise in the number of consultants and experts.”

The Century 16 movie theater in Aurora, Colorado where twelve people were killed and 70 injured in a 2012 mass shooting.

The definition also relies on public interest and intent

A big point of controversy that arises when we talk about mass shootings is our country’s uncomfortable history with mass murder in general. Some critics point to incidents like the Sand Creek Massacre, which took place in 1864 during the era of American Indian Wars. During the massacre, up to 163 Native Americans were killed by members of a Colorado Volunteer Cavalry.

They were shot, at the same place at the same time. It was, functionally, a mass shooting. But was it a mass shooting like we consider today?

Fox says no. “It was pseudo wartime,” he says. “We don’t count it because it was an official or unofficial act of war. What we do count are when individuals or small groups of individuals declare their own war, and turn a school, restaurant, movie theater or church into their own personal battleground.”

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It’s by that logic that the public doesn’t tend to think of events like the St. Valentine’s Day Massacre, in which seven men were gunned down by a gang controlled by Al Capone, as a typical “mass shooting.” It’s also the reason mass lynchings and other racial violence against black people in the post-Civil War era, or other high-casualty events of racial violence like the St. Louis “Race Riot” of 1917 or the Tulsa Massacre of 1921 don’t tend to get folded into that number.

Not only are the perpetrators, the victims and the nature of the casualties hard to quantify, it could be argued that the motives, while horrifying in their own right, fall outside of the scope of more modern definitions of “mass shooting.”

If that seems like splitting hairs or dismissing history, Fox offers another line of thinking for why we tend to think of mass shootings in a modern sense: Our own experiences and, perhaps, our own fear.

“A significant portion of America wasn’t alive in, say, the 1940s, so part of it is just a function of memory,” he says. “The bigger part has to do with technology and media. When these things happened, maybe we saw some grainy film days later, but we certainly didn’t hear it like we do now. There weren’t satellite trucks that would rush to the scene of a mass shooting and carry images of carnage right into our living rooms, making it feel like it’s happening just down the street.”