As gun control advocates call for tougher state and federal laws, much of the debate centers on the effectiveness of regulation designed to minimize deaths caused by firearms.
Proponents of gun control argue that common sense calls for tougher laws to stop gun violence. Gun rights advocates counter by noting that gun laws don't stop someone intent on breaking those laws from killing people.
So, do gun laws work?
While research on the subject is limited, the answer seems to be that states with stricter gun regulation have fewer firearms deaths — in some cases dramatically fewer — than those that don't.
But while the correlation is clear, there is little hard evidence of cause and effect.
The relationship between gun laws and firearms deaths is compelling. In states like Alabama,. Alaska and Louisiana, where guns are lightly regulated, the rate of deaths by firearms (per 100,000 people) is more than four times higher than in New York, Connecticut, Hawaii or Massachusetts, which have some of the strictest gun laws in the country.
The data come from the Centers for Disease Control and Prevention, which tracks firearms deaths, and a project at the Boston University School of Public Health, which tracks dozens of different provisions of gun laws in the 50 states.
Other research has also found a clear connection between stricter state gun laws and a lower rate of firearms-related deaths.
In 2013, researchers at Boston Children's Hospital and the Harvard T.H. Chan School of Public Health found that states with more gun laws had fewer gun-related deaths. The impact was seen for overall deaths, as well as for specific categories such as homicides and suicides.
But while the researchers confirmed that states with tougher gun laws have lower gun-related death rates, the study did not explain whether gun laws were the reason for the difference.
"As our study could not determine cause-and-effect relationships, further studies are necessary to define the nature of this association," they wrote.
While the cause and effect may seem intuitively obvious, there are apparently other factors behind the difference in gun-related deaths from one state to another.
In Maine, for example, where there are relatively few gun laws on the books, there were a little more than 8.3 gun-related deaths per 100,000. But Louisiana, with roughly the same number of gun laws, saw a firearms death rate of 21.3 in 2016.
On the other hand, the firearms-related death rate in Maine, with just 12 gun-related provisions, was roughly the same as in California, with more than 100 separate regulations governing gun ownership and use.
Researchers have speculated on possible explanations. Separate research, for example, has shown that gun-related suicides are higher in rural areas. Rates of gun deaths in rural states may also be higher because delays in getting medical treatment could lead to higher mortality rates from gun-related injuries.
While further study into the causes of gun violence may be needed, researchers won't get much government support unless Congress votes to overturn a 1996 law that barred support of firearms research by federal agencies.
The firearms research ban was introduced by Rep. Jay Dickey, R-Ark., on behalf of the National Rifle Association, after the CDC published a study which concluded that people who kept guns in their homes faced a nearly threefold greater risk of homicide and a nearly fivefold greater risk of suicide. Since then, the so-called Dickey amendment has brought federal funding of firearms research to a halt.
It remains to be seen whether the recent outcry over the latest school shooting in Parkland, Florida, generates enough political momentum to overturn the funding ban.
But before he died last year, Dickey apparently had a change of heart. In 2012, he co-authored a Washington Post editorial with Mark Rosenberg, the head of the CDC when the Dickey amendment was passed, calling for more scientific research to prevent firearm injuries and deaths.
"We were on opposite sides of the heated battle 16 years ago, but we are in strong agreement now that scientific research should be conducted into preventing firearm injuries and that ways to prevent firearm deaths can be found without encroaching on the rights of legitimate gun owners," they wrote.