In 2013, Barack Obama proposed changes to US gun law and was dramatically defeated. We analyze the possible effect of those policies in the 20 largest mass shootings of this year

Last Wednesday, two mass shootings happened in America. In one of them, 14 people were killed and 21 others were injured, prompting Barack Obama to describe stronger background checks for gun purchases as “common sense”. Earlier that same day, two gunmen killed one person and injured three others in Savannah, Georgia. In neither case is there any evidence that the killers obtained their guns illegally.

That’s not surprising. A Guardian analysis of the 20 shootings with the most fatalities in 2015 found that most gunmen obtain their weapons legally. But had a range of proposed federal reforms designed to strengthen gun laws been in place, many of those mass shootings could have been less likely to have happened. In nine of the 12 cases where information was available, tougher laws could have prevented killers from obtaining their guns.

Facebook Twitter Pinterest In the chart above, green indicates ‘yes’ and red ‘no’. Gray boxes indicate no information is available to answer the question. Numbers refer to the shootings ranked by number of fatalities, with 1 being the deadliest. Photograph: Mona Chalabi

To fully understand the impact of America’s gun control measures, it’s important to look beyond the handful of mass shootings that acquired enough headlines to puncture national consciousness. The most thorough source that currently exists is Mass Shooting Tracker, a collaborative project where users find and verify media reports to count the number of US mass shootings each year. The group defines a mass shooting as an incident where four or more people are shot – the injuries do not have to be fatal for the shooting to be included in their database.



In 42% of the 353 mass shootings recorded in 2015 so far, there were no reported fatalities. An additional 47% of those mass shootings resulted in between one and three people killed. But it’s harder to understand the role of gun control legislation in those mass shootings with fewer victims – often the shooters’ names aren’t known, let alone whether they had a criminal record or which guns they used. When only three Americans die, shootings usually aren’t remembered by the names of the locations where they took place.

Killings like the ones in San Bernardino, Charleston or Umpqua Community College make up a small fraction of all shootings that happen in the US but they represent a large part of publicly available information about mass shootings. The government doesn’t keep a database on gun deaths, let alone deaths from mass shootings. And media reports on most everyday shootings do not contain sufficient detail to answer questions about how the shooter got their gun. Because of that constraint, this analysis looks at how policy might have affected the 20 mass shootings that resulted in the most fatalities in 2015.

In 2013, Obama attempted to overhaul US gun law. The proposed legislation was designed to reduce the likelihood of another shooting like the one in Newtown, which had killed 20 children and six adults just four months earlier.

The Senate either blocked or defeated every single proposal. If they hadn’t, would the 20 worst mass shootings this year have been less likely? The answer is a cautious “yes”.

Legally obtained weapons

In nine of the 20 worst mass shootings so far this year, it’s a matter of public record that the gunmen obtained their weapons by legal means. In the remaining 11 cases, there’s no evidence to suggest that the guns were procured illegally.

Under US law, however, some of the killers should never have been able to make those seemingly legal purchases. Since he had previously admitted to drug possession, Dylann Roof should have been prevented from buying the .45-caliber he used to kill nine people in Charleston. A series of failures meant that FBI background checks did not prevent Roof from purchasing the murder weapon.

Assault weapons

Three of the 20 worst mass shootings in 2015 would not have been committed with legal weapons had the law been changed in 2013. One of Obama’s key proposals was to reinstate and strengthen the federal ban on assault weapons that was in place for ten years from 1994 – weapons which were used by three of the killers in this analysis.

In another eight of the 20 cases, it’s known that assault weapons were not used (most often those killers used handguns) and in the remaining nine cases, we were unable to find information about which weapons were used.

Magazines

Another very concrete legal change that was proposed in 2013 was to limit ammunition magazines to ten rounds. In 17 of the 20 worst mass shootings, the size of the magazine on the weapon has not been mentioned in media reports (in some cases, more than one weapon was used, which makes this information even harder to find). In all of the remaining three cases, research on the model and manufacturer of the weapons used indicates the guns had more than 10 magazine rounds. In the San Bernardino shooting, which killed 14 people, a Smith & Wesson M&P assault rifle was used. The weapon, according to Smith & Wesson’s site, boasts a 30-round magazine.

Facebook Twitter Pinterest Smith & Wesson M&P assault rifle, as advertised on their site. Photograph: Smith & Wesson, 2015

Criminal records

The killers’ previous criminal records are rarely known. The only case that can be ruled out of the 20 most deadly is that of the San Bernardino attackers: the chief of the San Bernardino police department said he was not aware of the suspects having any previous contact with law enforcement.

In five cases, the killers were known to have a criminal record.

One of them was David Conley. In August, Conley entered his ex-girlfriend’s house in Texas through an unlocked window, gathered her husband, six children and herself into a master bedroom, then handcuffed and executed them one by one with a 9mm pistol. As well as auto theft, cocaine possession and evading arrest, Conley’s criminal record included an incident with Valerie Jackson, the ex-girlfriend he eventually killed. In a domestic violence case, Jackson told police that Conley had cut her, punched her and wrapped an electrical cord around her baby’s neck. Indeed, sheriff’s deputies made at least two welfare checks during the multi-hour ordeal in which Conley killed eight people. They apparently left when no one answered the door.

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In eight of the 20 worst mass shootings this year, there is no information about how any of the measures proposed in 2013 might have made a difference. Those gray areas are even more common in mass shootings like the Conley murder, where the killer was known to the victims.

Evaluating some policy proposals, such as the question “were armor-piercing bullets used?”, suggests it’s likely that those gray boxes above would turn red if information were available. However, on other questions, such as whether the weapon was bought privately and whether the gun had more than 10 rounds, more information would likely reveal that some of the 20 worst mass shootings could have been affected by legislative changes that were proposed in 2013.

Overall, the picture suggests that tougher gun control measures could have reduced the likelihood of some of the worst mass shootings this year. But the analysis also shows that what we don’t know about the impact of gun control is far more than what we do know.

That’s partly because while San Bernardino might be remembered, the other mass shooting which took place less than 12 hours earlier that same day probably won’t be. That’s true of most of the 353 mass shootings that have happened this year and the hundreds more that will likely happen in the year to come. We won’t know how they obtained their weapons and we won’t know how US gun law impeded or facilitated their crime.