States with a heavier dose of firearm laws tend to have the lowest rates of gun deaths, according to a study released Wednesday by Boston-based researchers who argue their findings show "there is a role" in America for more rigid gun-control legislation.

"It seems pretty clear: If you want to know which of the states have the lowest gun-mortality rates just look for those with the greatest number of gun laws," said Dr. Eric W. Fleegler of Boston Children's Hospital who, with colleagues, analyzed firearm-related deaths reported to the Centers for Disease Control and Prevention from 2007 through 2010.

By scoring individual states simply by the sheer volume of gun laws they have on the books, the researchers noted that in states with the highest number of firearms measures, their rate of gun deaths is collectively 42 percent lower when compared to states that have passed the fewest number of gun rules. The study was published online in the journal JAMA Internal Medicine.

As proof, Fleegler pointed to the firearm-fatality rates in law-laden states such as Massachusetts (where there were 3.4 gun deaths per 100,000 individuals), New Jersey (4.9 per 100,000) and Connecticut (5.1 per 100,000). In states with sparser firearms laws, researchers reported that gun-mortality rates were higher: Louisiana (18.0 per 100,000), Alaska (17.5 per 100,000) and Arizona (13.6 per 100,000). 

In Arizona -- just as the new study was released -- former Rep. Gabrielle Giffords returned Wednesday to the grocery store where she was shot and urged Congress to expand background checks for gun purchases. She told the gathered crowd and U.S. lawmakers to: "Be bold. Be courageous. Please support background checks." 

On Thursday, the Senate Judiciary Committee is expected to vote on a bill that would stiffen penalties for people who purchase guns illegally for others, and to make gun trafficking a felony. 

Fleegler and his team openly acknowledged they could not prove a definitive "cause-and-effect" link between tighter laws and a lower risk of gun-caused homicides or gun-related suicides. But ahead of the expected Senate vote, the researchers said they did determine this:

In those states that have the most firearm laws, those states also have the lowest rates of household-firearm ownership.

"And states that have the lowest gun-ownership rates also have the lowest gun-mortality rates," Fleegler said. "So states that try to have gun laws that are meant to be meaningful, they seem to be able to actually have an impact. That’s an important thing to learn from."

The findings were quickly challenged by two critics,  a top gun-rights advocate and a leading expert on the nexus of public health and gun policy, who each questioned the merits of the Boston findings and the rigor of the science behind the study.

It sounds to me like some sort of sleight of hand from a political sense," said Dave Workman, senior editor at Gun Week magazine and director of communications for the Citizens Committee for the Right to Keep and Bear Arms, in Bellevue, Wash.

"If they are dancing around this cause and effect, I'm not sure that the public should warm up to that kind of a conclusion because it really doesn't conclude it, it only suggests or intimates something," said Workman, who served three terms on the National Rifle Association board of directors.

"It's presumably the result they wanted to get in order to have the public believe something. Is that fair? Is that good science? Is that good research? I don't know." 

Workman further argued that in states or jurisdictions where gun laws "make it difficult for law-abiding citizens" to buy firearms through legal channels, "that does not necessarily translate to lower fatalities."

"And, as proof," he added, "I give you the city of Chicago." 

In an accompanying commentary, Dr. Garen J. Wintemute of the University of California, Davis, Sacramento, wrote that the paper's conclusion "would be an important finding — if it were robust and if its meaning were clear."

Ultimately, Wintemute wrote, the new study provides no insights on the key questions facing Congress: "Do the (gun) laws work, or not? If so, which ones?"

"Correlation does not imply causation," Wintemute said in a phone interview. "The plain English way of saying this is: Just because two things exist at the same time, that does not mean one thing caused the other. That's what's being implied here. All they counted in that analysis was the number of laws in each state, not which laws. There's no information in this study on the specifics of the (state) laws and whether they were enforced or not."

"So in a sense, the only conclusion you could draw would be: Pass more more laws but it doesn't matter which ones or what they're intended to do," Wintemute said. "That's just silly." 

Fleegler's study was not related to a recent executive order by President Barack Obama lifting a ban on gun violence research funded by federal agencies such as the CDC. Fleegler said he used public data at no cost to conduct his analysis. 

Wintemute said the study actually underscores the need for well-funded research into the effects of gun violence on public health. 

"Until we revitalize firearm violence research, studies using available data will be the best we have. They are not good enough."

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A little-known kibosh on government research into the public health effects of gun violence is expected to be lifted after President Barack Obama called Wednesday for renewed scientific inquiry -- and funding -- to address the problem.

Obama issued a presidential memorandum directing the Centers for Disease Control and Prevention and other scientific agencies to research the causes and prevention of gun violence -- and he called on Congress to provide $10 million to pay for it.

"We don't benefit from ignorance. We don't benefit from not knowing the science from this epidemic of violence," he said.

The move effectively reverses 17 years of what scientists say has been a virtual ban on basic federal research and is part of a package of new gun control policies aimed at reducing gun violence after tragedies such as the shootings last year in Aurora, Colo., and Newtown, Conn. It would encourage research including links between video games, media images and violence.

The action immediately was praised by scientists who said pro-gun advocates -- including the National Rifle Association -- had choked off funding for CDC firearms research starting in the mid-1990s and imposed a chilling effect on those who dared to pursue it.

"He's saying this is very important and I'm going to back you on this," said Dr. Mark Rosenberg, president of the Task Force for Global Health and director of the CDC's Center for Injury Prevention and Control from 1994 to 1999. "Basically, they've been terrorized by the NRA."

From the mid- 1980s to the mid-1990s, the CDC conducted original, peer-reviewed research into gun violence, including questions such as whether people who had guns in their homes gained protection from the weapons. (The answer, researchers found, was no. Homes with guns had a nearly three times greater risk of homicide and a nearly five times greater risk of suicide than those without, according to a 1993 study in the New England Journal of Medicine.)

But in 1996, the NRA, with the help of Congressional leaders, moved to suppress such information and to block future federal research into gun violence, Rosenberg said.

An amendment to an appropriations bill cut $2.6 million from the CDC’s budget, exactly the amount the agency’s injury prevention center had previously spent on gun research. The money was returned to the agency later, but targeted for brain injury trauma research instead.

In addition, the statute that governs CDC funding stipulated that none of the funds made available to the agency can be used in whole or in part “to advocate or promote gun control.”

While that did not specifically prohibit firearms research, the language was ambiguous enough to alarm CDC officials and stifle scientists interested in gun data, said Stephen Teret, director for the Center for Law and the Public’s Health at the Johns Hopkins Bloomberg School of Public Health.

“CDC overreacted to that statement and became more reluctant to fund anything dealing with guns, even the traditional epidemiological research, so there was a chilling effect,” Teret said.

The NRA attacked some scientists, trying to discredit their research, endangering their jobs and even threatening their families, Rosenberg claimed.

“These were not mild campaigns,” he said. “When the NRA comes after you, they come after you with both barrels.”

Officials with the NRA did not return NBC News requests for comment.

The dearth of basic data means that policymakers and the public know little about the causes of gun violence that kills about 32,000 people in the U.S. each year. At the same time, Teret said, research into other public health problems such as automobile deaths has yielded dramatic results.

“When I first started, there were 50,000 people a year dying on the highways. Now it’s 32,000 and that’s because there’s been superb scientific research,” Teret said. “We need to be able to address gun-related injuries in the same scientific manner as highway injuries.”

Obama’s directive will immediately impact federal agencies that engage in scientific research about gun violence, said Health and Human Services Secretary Kathleen Sebelius. 

"We are committed to re-engaging gun violence research at the Centers for Disease Control and Prevention and the National Institutes of Health," she said in a statement. 

The move may restore the will to research gun violence, but it will be up to Congress to supply the funding to carry it out, the scientists noted.

If that happens, there are talented researchers poised to pursue the projects, said Dr. Frederick Rivara, a pediatrician and editor of the Archives of Pediatrics and Adolescent Medicine.

He estimated that if CDC were given the green light for research now, scientists could have meaningful results that could be used to shape public policy within a year or two.

“We’ve lost almost 20 years of really waiting around,” said Rivara. “Given how large a public health problem this is, it’s a tragedy.”

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NEWTOWN, Conn. – Police Chief Michael Kehoe has a message for the White House: “Ban assault weapons, restrict those magazines that have so many bullets in them, shore up any loopholes in our criminal background checks,” he said in an exclusive interview with NBC News.

As Vice President Joe Biden prepares to present his gun violence proposals to the White House this week, the residents of Newtown — including first responders and some families of the victims — are speaking out on gun policy for the first time.

Few have a more personal connection to the issue than Kehoe: He was one of the first on the scene at the Sandy Hook Elementary School on Dec. 14 after reports came in of a shooting. He says he’s still haunted by flashbacks of what he witnessed when he entered the school from the rear -- the eerie silence in the hallways, the smell of burnt gunpowder and then the bodies of dead children on the floor of the classrooms.

“I was sickened. I was angry,” he said. “It was something I never could have imagined could have happened in any school in Newtown.”

But as a veteran law enforcement officer, what was most striking to Kehoe was that the gunman, 20-year-old Adam Lanza, had heavier firepower than Kehoe and his officers. The police had Glock pistols with 14-round magazines;  Lanza had a Bushmaster assault-style rifle, two handguns and multiple 30-round magazines that allowed him to squeeze off an estimated 150 shots.

Although it’s still not clear if Lanza ever fired at responding officers — Kehoe thinks he took his own life when he heard the police sirens —  the disproportionate balance in firepower bothers him.

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Newtown, Conn., Police Chief Michael Kehoe at a news briefing on Jan. 2.

“We never like to think we’re going to be outgunned in any situation we’re dealing with," he said. “We do a good job of  securing dynamite in our society. … (Assault rifles) are another form of dynamite. … I think they should ban them.”

Kehoe’s comments come as a new grassroots group — called Sandy Hook Promise — is planning a news conference  Monday in which residents of Newtown and some of the victims’ families plan to call for a “national conversation” on gun violence, mental health and school safety. The goal: to prevent “similar tragedies from ever taking place again.”

But there is far from unanimity about what should be done about guns.

Marie-Claude Duytschaever, the grandmother of 6-year-old Noah Pozner, the youngest victim that day, said she, too, wants a ban on assault rifles.

“Noah had the right to go to school safely,” she said. “He had the right to live, to have a job and a normal life. I think that’s more important than to have a gun that can obliterate a whole room in seconds.”

Sandy Hook Promise group will not call for specific gun control measures at Monday’s press conference and a few have expressed concerns that the White House is moving too rapidly with its proposals — and without seeking input from the families of the victims of Newtown.

The national headquarters of the National Shooting Sports Foundation — the trade association and lobbying arm of gun manufacturers — is just down the road from the Sandy Hook Elementary School. Its representatives met with Biden’s task force last week, and this week it will hold its annual SHOT SHOW in Las Vegas, an event at which major gun makers get to exhibit their wares.

The group didn’t respond to requests for comment. But last week it posted this statement on its website: “Semi-automatic firearms are now the most popular type of firearm in America and are used for a wide variety of legitimate sporting purposes, including hunting, small game control, target shooting and personal defense. They should not be banned.”

It is not clear whether Biden will include a ban on assault weapons in the proposals he submits this week. Any effort to ban the rapid-fire rifles in the United States is expected to face tough opposition in Congress.

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