A new analysis of 56 mass shootings across America since 2009 finds women and family members are the most frequent victims, and that the shooter almost always acquired his guns legally, in cases where the gun source is known.

“In at least 32 of the cases (57 percent), the shooter killed a current or former spouse or intimate partner or other family member, and at least eight of those shooters had a prior domestic violence charge,” the Mayors Against Illegal Guns report on mass shootings said, suggesting that the problem of gun violence is far more related to violence against women in homes than rampages in public settings such as schools and theaters.

The study also found that in the cases where the source of the guns was known, almost all were acquired legally: only two examples were given of mass killings with a stolen or illegal gun. That finding runs counter to the gun lobby’s oft-cited rhetoric that only criminals abuse guns.

“We had sufficient evidence to judge whether the shooter was a prohibited gun possessor in 42 of the 56 incidents,” the report said, referring to laws barring ex-felons, mentally ill people, drug addicts and other categories of people from owning guns. “Of those 42 incidents, 15 (36 percent) involved a prohibited possessor and 27 (64 percent) did not.”

MAIG's analysis should help focus the national debate about curbing gun violence, whether the most horrific mass shootings or ongoing violence where 33 Americans are killed daily from guns (not counting suicides). The report strongly suggests that better background checks before buying guns are needed, as well as far more discussion of domestic violence and violence against women.

“It’s clear in the public’s mind that background checks can help to prevent some of these killings,” said Erika Soto Lamb, spokesperson for Mayors Against Illegal Guns. “Because as we found with the domestic violence situations, there are 38 percent fewer killings of women in states that require background checks for every handgun sale.”

The gun-control group relied on FBI data and media reports to identify 56 mass shootings between 2009 and January 2013, where four or more people perished. These headline-grabbing incidents are less than 1 percent all gun-related deaths, the report said. Not surprisingly, assault weapons—where bullets can be rapidly fired without reloading—were tied to the deadliest shootings.

“Assault weapons or high-capacity magazines were used in at least 13 of the incidents (32 percent),” the report said. “These incidents resulted in an average of 14.8 total people shot—135 percent more people shot than in other incidents (6.8)—and 8.0 deaths.”

The debate before Congress has mostly focused on restricting the hardware used in the worst mass shootings, such as the types of guns and ammunition-holding magazines. While there have been calls for better background checks, including a renewed emphasis on mental health screening, the report found that shooters with mental health diagnoses known to courts, where they had been adjudicated as mentally ill, or involuntarily committed, was not very common.

“In four of the 56 incidents, we found evidence that concerns about the mental health of the shooter had been brought to the attention of a medical practitioner, school official or legal authority prior to the shooting,” the report said.

In contrast, the incident descriptions listed 26 shooters whose rampages ended by committing suicide, suggesting that their mental health was certainly unbalanced, although it did not provoke a sufficient earlier response that might have prevented the killings. That gap underscores the difficulty in reporting mental health issues, which are heavily regulated under medical privacy laws.

“It is low—but we know why,” Soto Lamb said.

The most striking feature of the MAIG report were the descriptions of domestic violence—in all but two cases by men—who were targeting women: new wives, ex-wives, girlfriends, mothers, and then others in close family circles. It that found 32 of the 56 mass shootings (56 percent) "took place wholly in private residences." Less than one-quarter "took place entirely in public spaces."

“The shooter killed his wife and their five children before killing himself,” said the report’s oldest account, from Delaware in January 2009.

“The shooter killed his parents and three siblings in their home,” the report’s newest account, from New Mexico this January, said. “He then loaded a van with guns and ammunition with the intent to kill his girlfriend’s family and die in a shootout at Walmart.”

“The shooter killed his mother in her home and then traveled to a nearby elementary school where he shot 28 people, killing 26 of them,” it said in the second newest account, referring to December’s Sandy Hook Elementary School shooting.

Soto Lamb said Congress’ unfolding gun control debate has to be enlarged to include domestic violence and the daily deaths of 33 Americans, not just the most horrific mass shootings. She also said it was a “conundrum” that most of the domestic violence incidents are inside homes, because the U.S. Supreme Court’s 2008 Heller ruling expanded the U.S. Constitution’s Second Amendment to include the right to keep a handgun at home for self-defense.

“More than half of the women murdered with guns in the U.S. were killed by intimate partners or family members. It’s 64 percent,” she said. “We have data and information that the presence of a gun in a domestic violence situation increases the risk of homicide for women by 500 percent.”