The mass shooting in Plano, Texas, this month was the deadliest of 2017. It also fit a pattern: The shooter had targeted his estranged wife and her friends and family—and had a history of intimate partner violence (IPV).

Now, a new study led by Boston University School of Health (BUSPH) researchers has found that some restricting firearm possession by people at high risk of committing abuse are associated with significantly lower rates of intimate partner homicide (IPH).

Writing in the Annals of Internal Medicine, the researchers looked at states that went beyond federal law to require people with restraining orders to relinquish firearms in their possession. They found IPH rates were 9.7 percent lower in states with these laws, and firearm-specific IPH rates were 14 percent lower. "There were 75 fewer IPH deaths in the US in 2015 among states with firearm relinquishment laws than would have been expected in the absence of these laws," the authors wrote. "Also based on the model, if all 50 states had such laws in place, there would have been an additional 120 fewer IPH deaths across the nation in 2015."

"This is one of the first studies to demonstrate that it's not enough to just pass a gun law," says Michael Siegel, professor of community health sciences at BUSPH and the study's senior author. "You have to build effective enforcement procedures into the law in order for it to have its intended impact."

Every year, more than 1,800 people in the United States are killed by their intimate partners. About half of those homicides are committed with firearms, and 85 percent of the victims are women. A majority of mass shooting victims from 2009 to 2015 were an intimate partner, ex-partner, or other family member of the shooter, according to Everytown for Gun Safety, and the perpetrators of several high-profile mass shootings—in Mississippi over Memorial Day weekend this year, at the Pulse nightclub in 2016, and in a Planned Parenthood clinic in Colorado Springs in 2015—also had histories of domestic violence.

To prevent IPH, the federal 1994 Violence Against Women Act bars firearm possession by anyone subject to permanent IPV-related restraining orders. However, offenders who already had guns in their possession were not required to surrender them.

To examine the state laws that have sought to close this "relinquishment gap" loophole, the investigators used data from the Federal Bureau of Investigation's Supplementary Homicide Reports from 1991 to 2015.

They found the national IPH rate fell more than 50 percent from 1991 to 2015, as did the firearm-related IPH rate. However, they also found a nearly five-fold range in average IPH rates across the states in 2015, with the lowest in Minnesota and the highest in Louisiana, with IPH-related gun laws associated with lower rates.

"The NRA has long argued that we don't need more laws, we just need to enforce the laws that we already have," Siegel says. "This study shows that there may be some truth to that. Adding an enforcement provision—required relinquishment of firearms—to an existing law that prohibits gun possession by people subject to restraining orders appears to turn it from a law that has limited impact to one that saves lives."

The researchers write that only three previous studies have evaluated the impact of these state laws on IPH, but none since 2003, before the reauthorization of the Violence Against Women Act in 2005 spurred a sharp increase in the number of these laws.

As of 2016, 11 states explicitly required people convicted of an IPV-related misdemeanor to surrender their firearms after conviction, and 15 states explicitly required people subject to an IPV-related restraining order to surrender their firearms for as long as the court order was in effect.

The authors note three —Washington, Alabama, and Arkansas—repealed IPH prevention gun laws during the 25-year study period. The findings come at a time when are weakening and gun violence research is more hampered than ever, and with funding for the National Institutes of Health (NIH) gun violence research program allowed to lapse earlier this month.

Journal information: Annals of Internal Medicine

Provided by Boston University School of Medicine