Gun sales in the United States spiked dramatically after a shooter walked into Connecticut's Sandy Hook Elementary School on lunch wagon sex videoDec. 14, 2012 and killed 26 people, 20 of whom were children. Now researchers say that as a result of that rush in gun purchases, 60 additional Americans — 20 of whom were children — were killed by accidental gunshots in the five months following the tragedy.

Five months after the shooting, three million more guns than usual left U.S. stores and entered people's homes (or wherever they chose to keep them). In a study published Thursday in the journal Science, researchers show that the spike in accidental gun fatalities was almost certainly caused by this simultaneous increase in the number of guns generally around, and apparently not locked up properly.

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"I can’t come up with a better alternative explanation other than increased exposure to guns causes this," Aaron Kivisto, a forensic psychologist and gun violence researcher at the University of Indianapolis who was not involved in the study, told Mashable. "It’s compelling evidence."

Original image has been replaced. Credit: Mashable

It's true that lots of Americans accidentally shoot either themselves or others, regardless of any significant spike in gun purchases. For a typical five-month window in the U.S., this number averages about 210 fatalities. But during the same five-month period in which there was an added spike of three million guns sold, there was an additional spike of 60 more accidental deaths.

The researchers also turned to Google to see how Americans were searching online for where to buy a gun and how to clean a gun between 2010 and 2014. Again, there was a spike in the months following the Sandy Hook shooting. The search terms "buy gun" and "clean gun" surged during this period.

For the study's researchers, the alignment of this data is enough to show that an increase in accidental gun deaths resulted from more guns being around and is not simply a link (or correlation) between the two events.

"The goal was to be able to distinguish causality from correlation," Robin McKnight, the study's co-author and a health economist at Wellesley College, told Mashable. "Our conclusion is that it is a causal effect of the gun exposure."

Original image has been replaced. Credit: Mashable

Unlike laboratory experiments to see if a certain medicine works, you can't set up an experiment to test if people will accidentally shoot themselves, so a compelling alignment of events may be as good as we can get.

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"This is a field where true experiments are impossible," said University of Indianapolis researcher Kivisto. "It’s correlation data that would be consistent with causation."

Noam Ostrander, a gun violence expert and chair of DePaul University's Department of Social Work, agrees. "I was convinced by their argument and their analysis," he told Mashable. "It doesn’t seem that they’re overstating their findings."

However, Ostrander notes that "their study is probably incredibly conservative," as the researchers only looked at unintentional deaths. "If they were able to look at non-fatal gunshot wounds during that time, it’s likely they would have seen an additional spike in those."

These are surely grim statistics, but they come with a clear solution.

"For me, the big picture is that it really highlights the importance of safe gun storage," said study co-author McKnight. This is especially important if there are curious children around guns. Unfortunately, many Americans can't get this right.

As for what causes a spike in gun sales following a massacre of children in the U.S., McKnight believes it's not the traumatic shooting event that motivates people to buy more guns, perhaps for protection. Instead, it could very well be talk about gun policy, or in some cases, gun control.

"I think that the increase in gun exposure we see has to do with policy gun discussion rather than the incident themselves," says McKnight.

Two specific incidents, both involving President Obama, support this idea. On both Jan. 12 and Feb. 13, 2013, Obama spoke about potential gun control legislation, including new proposals for background checks to decrease the likelihood of unstable individuals buying guns. During both events, there were notable spikes in people searching Google for "buy gun" and "clean gun."

Regardless of the cause, three more million guns entered U.S. homes, and many of those guns, regrettably, were left unattended.

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