Why is it so difficult to stop mass shootings in the U.S.?

JUDY WOODRUFF: Mass shootings make up a small fraction of overall gun violence in the country, but the FBI counted more than 170 cases of mass killings between 2006 and 2011.

USA Today has been tracking those cases and the connection with guns. Their reporting team found the official count is understated.

Meghan Hoyer is a data reporter working on the project. And she joins me now.

Meghan Hoyer, welcome.

MEGHAN HOYER, USA Today: Thank you.

JUDY WOODRUFF: So, first of all, define quickly what you mean by mass killing.

MEGHAN HOYER: Sure.

A mass killing is basically four or more dead, not including the shooter. So — and that's the FBI's original definition.

JUDY WOODRUFF: And, so, technically what happened last night in Louisiana wouldn't be considered a mass killing?

MEGHAN HOYER: Right. That might be considered a mass shooting, but not a mass killing. We were just interested in the four or more dead.

JUDY WOODRUFF: Let's talk about what you learned about the people who do those shootings. Who are they?

MEGHAN HOYER: Sure.

They're overwhelmingly male; 94 percent of the cases were men. Their average age is about 30, but it really ranges. We had teenagers to older adults. Men tend to use more guns. Women tend to kill in other ways, arson, drownings, things like that.

JUDY WOODRUFF: And what did you learn about the circumstances, about who the victims are, how these things typically — or is there a pattern?

MEGHAN HOYER: There's not necessarily a pattern, but there are certain things that stand out.

More than 50 percent are family-related, so and in…

JUDY WOODRUFF: More than 50 percent?

MEGHAN HOYER: More than 50 percent. In more than half — in well more than half the cases, the victim knew their shooter.

So, these cases where it's a public shooting in a public place and it's a stranger-on-strange crime, that doesn't happen very much. That's only about 15 percent of these mass killings. The vast majority are family cases. They happen inside the home.

JUDY WOODRUFF: And yet we saw — and in fact what we saw in the last week, killings that didn't get the kind of publicity that the shootings in Chattanooga, this one in Louisiana, there were family — families involved.

MEGHAN HOYER: Exactly. Yes.

There were five mass killings this week. That doesn't include the shooting in the theater last night. Again, the majority of those were family killings, a family found dead in Modesto, a woman and her children, a family in Oklahoma where two teenagers have been arrested and the rest of their family has — was stabbed.

JUDY WOODRUFF: And, again, these are the kinds of things that often don't get the kind of attention.

MEGHAN HOYER: Right, they might get the regional attention, but they don't get the national buzz.

JUDY WOODRUFF: What about the guns that are used? What did you learn about whether they are gotten legally or not?

MEGHAN HOYER: Well, in terms of mass killings, about three-quarters of them are committed with guns. That means the other quarter of them are not gun-related at all.

Of the gun killings, what we have seen are that most guns are handguns. They are not these high-capacity assault rifles or high-capacity assault weapons that we hear so much about. We looked a little bit at legal vs. non-legal acquisition. In a majority of cases, they're acquired legally.

And even in cases where they're not, what experts say is that these are people who tend to be very determined. And where there's a will, there's a way. Even if they have been banned from getting guns, if they have a prior record, generally, they find a way to find a weapon.

JUDY WOODRUFF: Meghan Hoyer with USA Today, we thank you very much.

MEGHAN HOYER: Thank you, Judy.

JUDY WOODRUFF: Now to a series of conversations we're calling Guns in America.

We will talk with people intimately involved in the debate, coming to it from a variety of perspectives.

Tonight, we hear from retired NASA astronaut and Navy combat veteran Mark Kelly. His wife, former Congresswoman Gabrielle Giffords, was severely wounded after being shot in the head at an event in Tucson, Arizona, in January 2011. Gabby Giffords continues to recover from the shooting.

In the wake of the tragedy at Sandy Hook Elementary School, they founded the group Americans for Responsible Solutions as a way to bring attention to ways to make our communities safer.

Captain Kelly, we thank you for joining us.

MARK KELLY, Co-Founder, Americans for Responsible Solutions: Oh, you're welcome, Judy.

JUDY WOODRUFF: We don't have all the details about this shooting incident last night in Lafayette, Louisiana, but knowing what you know, your background on this, how do you respond to something like this?

MARK KELLY: Well, I think, you know, a logical response is that we have a lot of gun violence in this country.

We have — over 30,000 people die from gun violence every year. In states that have the weakest gun laws, we tend to have more gun violence. And Congress is perfectly capable of doing something about it. But they choose not to. And that's something that, you know, people should demand. They should demand action, because, unless we make changes to our laws and changes to easy access for felons, domestic abusers, people that are mentally ill, we will continue to see this very high rate of gun violence.

JUDY WOODRUFF: Well, what kinds of things should be done? Because we know — what we do know so far about the shooter in Louisiana is he did have some sort of criminal background. So, he was denied access. He wasn't allowed to buy or get a conceal-carry permit. But what kinds of changes need to be made?

MARK KELLY: Well, first of all, I don't know all the details. And I think it will take several days to come out.

Whether or not he was a convicted felon, you know, that should be pretty clear that we shouldn't allow convicted felons to get access to guns or domestic abusers or people who are dangerously mentally ill. If he fell into one of those categories, in the state of Louisiana or wherever, he had — was able to get this gun from, if they knew about it, then we have got to look as to why.

Maybe he went to a gun show where you don't need to get a background check. So, some clear things we can do, and I think we would all agree that keeping guns, dangerous firearms out of the hands of criminals is a good idea. We should all be able to agree on that.

But because of special interests in Washington, D.C., and other state capitals, our political leaders tend to be paralyzed on this issue.

JUDY WOODRUFF: Well, I know your group says, Americans for Responsible Solutions, you say there's a way to do this and still respect and adhere to the Second Amendment, in other words, there still be the right to have a gun.

So where do you draw the line? I mean, there's been — as you just said, it's been so hard to get anything done in Washington.

MARK KELLY: Well, responsible citizens or responsible gun owners should have access to guns for whatever reason they want, if it's to protect themselves, to go hunting, to go target shooting.

I'm a gun owner. Gabby's a gun owner. We don't want to negatively affect anybody's rights. And I don't think many Americans do. But, clearly, the easy access we provide to felons and criminals is something that really shouldn't exist. A simple background check can prevent not every one of these things from happening, but it can prevent some criminals who will commit crimes with these weapons from getting them.

So, that's pretty clear and it's obvious. And as an organization, we have made a lot of progress in a lot of different states. And we're hopeful that, in time, we're going to make progress on Capitol Hill.

JUDY WOODRUFF: Are you changing minds, though? Because we have seen shooting after shooting after shooting. And, as we just heard some of the statistics, in talking to the reporter from USA Today, it's a regular thing, and guns are the way people typically kill someone in this country or kill several people. Why has progress been so difficult?

MARK KELLY: Well, it's really because of a very powerful special interest in Washington, D.C., and in state capitals.

If you were to poll — like, let's do a big sample size national poll on something like background checks, and you will find that probably around 90 percent of Americans think you should get a background check before buying a gun. You know, the United States Senate could not pass the Manchin-Toomey background check bill.

I'm hopeful that they will someday. We're trying to convince them that that is the right thing to do. You know, we have 15 to 20 times the death rate from gun violence than any industrialized country. And the sad thing is, we're a country of laws, and we should be able to fix that. And we can fix that.

So, people need to write their congressman, write their governor, and build the support, and, in time, we will get this country back on the right track.

JUDY WOODRUFF: Captain Kelly, how much of this has to do with enforcing laws that are already on the books? We know the shooter in Charleston, South Carolina, they said shouldn't have been able to get a gun, but because the laws were not followed, records were not kept, he was able to get a gun. What about that?

MARK KELLY: Well, I think specifically with this case — I mean, this happened yesterday. So, I think it's going to take some time for all the facts to be out there.

But, clearly, when people are prohibited purchasers, sometimes, there are holes in that system. Sometimes, there are mistakes made. But I can tell you one big hole is the 40 percent of gun sales that are done without a background check that you can drive a truck through.

I mean, that's a huge hole that can be filled. We can fix that problem. And we can fix others. And we're not going to stop every one of these things from happening. But we could — we can put a pretty big dent in it. I mean, when you think about it, 33,000 people every single year die from gun violence in the United States. And that is an enormous number.

Imagine the steps we would take if suddenly we had 30,000 people dying in airplane accidents. I mean, we would go — we would make an enormous effort to do something about it. And we should be doing the same thing here.

JUDY WOODRUFF: Captain Mark Kelly, talking to us about the epidemic of gun violence in this country, thank you very much.

MARK KELLY: You're welcome, Judy. Thanks for having me on.

JUDY WOODRUFF: And in a press conference happening right now, police in Lafayette, Louisiana, say the shooter, John Russel Houser, bought the handgun he used legally at a pawn shop in Alabama in 2014.