Wednesday's shooting in Florida, like so many mass murders before it, seems likely to raise a debate we've had many times before: Why does the US have such a high rate of gun murders, by far the highest in the developed world? Is it because of guns, or is there something else going on? Maybe America is just more prone to crime, say, because of income inequality or cultural differences?

A landmark 1997 study actually tried to answer this question. Its findings — which scholars say still hold up — are that America doesn't really have a significantly higher rate of crime compared to similar countries. But that crime is much likelier to be lethal: American criminals just kill more people than do their counterparts in other developed countries. And guns appear to be a big part of what makes this difference.

Crime is not the problem

The seminal work here is a 1999 book by Berkeley's Franklin Zimring and Gordon Hawkins, called Crime Is Not the Problem. Zimring and Hawkins set out to examine what was, at the time, the conventional wisdom: that America had a uniquely terrible crime problem, one without any parallel in other developed democracies.

They found, pretty definitively, that the conventional wisdom was wrong. "Rates of common property crimes in the United States are comparable to those reported in many other Western industrial nations, but rates of lethal violence in the United States are much higher," they write. "Violence is not a crime problem."

Zimring and Hawkins determined this by looking at 20 developed countries' overall crime rate and rates of violent death. They found virtually no connection between the two, indicating that a country's level of violent death wasn't determined by its overall crime levels:

The lowest death rate country (England) has a crime rate just over average. The next lowest violence nation is Japan, which has the lowest crime rate also. The third lowest death rate country is the Netherlands, in the highest crime rate group.

"This data set provides a multinational example of the central point that lethal violence is the crucial problem in the United States," Zimring and Hawkins write. "It shows the United States clustered with other industrial countries in crime rate, but head and shoulders above the rest in violent death."

Why does this happen? It's not because, as you might think, American violent criminals are just more likely to kill people. "Only a minority of Los Angeles homicides grow out of criminal encounters like robbery and rape," they find (there's no reason to believe the pattern would differ in other cities). So even if it could be shown that American robbery and rape rates are across-the-board higher than those in similar countries (which doesn't appear true today), that still wouldn't explain why America has so many more homicides than other countries.

Again, Zimring and Hawkins's LA data was revealing. "A far greater proportion of Los Angeles homicides grow out of arguments and other social encounters between acquaintances [than robbery or rape]," they find.

This is where guns enter the story. The mere presence of firearms, according to Zimring and Hawkins, makes a merely tense situation more likely to turn deadly. When a gang member argues with another gang member, or a robber sticks up a liquor store, there's always a risk that the situation can escalate to some kind of violence. But when people have a handheld tool that is specially engineered for killing efficiently, escalation to murder becomes much, much more likely.

And indeed, that's what Zimring and Hawkins's data found.

"A series of specific comparisons of the death rates from property crime and assault in New York City and London show how enormous differences in death risk can be explained even while general patterns are similar," they explain. "A preference for crimes of personal force and the willingness and ability to use guns in robbery make similar levels of property crime fifty-four times as deadly in New York City as in London."

Guns, not criminality per se, are the problem.

Guns are still the problem today

In a 2015 email to Vox, Zimring contended that Crime Is not the Problem's core argument remains true despite a significant international drop in overall crime rates since the book was published.

"There has been quite a bit of work on these issues in the 18 year[s] since the book was published," he wrote, "and it confirms the basic argument rather powerfully."

The data seems to support this. "Robbery and assault rates ... reveal several Western nations that rival the United States," a 2011 review found. "While the level of lethal violence in the United States is probably the highest in the Western world, it is hard to make the case for US exceptionalism when it comes to non-lethal violence."

Harold Pollack, co-director of the University of Chicago's Crime Lab, called Zimring and Hawkins's book "an excellent source." In a 2015 phone interview, he pointed to a number of more recent studies that fit the pattern it identified.

"There's no question the United States faces a number of distinctive social policy challenges, some of which affect the crime rate. But many other OECD countries face their own distinctive problems that affect their crime rate," he told me. Western Europe, for example, has a major problem with drug use. Canadian cities have "very high" rates of property crime like car theft. And yet, the US still stands out on murders.

"I think that Americans have this view of Western Europe, or Toronto for that matter, which is very stereotypical and doesn't take into account the challenges that many of peer industrial democracy problems face," he points out. "There's a lot of drug sale, a lot of ethnic stratification and conflict, there's a lot of just general crime."

Pollack also shared Zimring and Hawkins's theory of the ease with which guns escalate conflict to violence, and thus heighten homicide rates. "Some of the behaviors that we think of as fundamentally linked with violence may stay quite steady as the violence rate goes down, as you get a better handle on the gun issue," he explained.

New York's recent tightening enforcement of gun laws serves as a good example. According to Pollack, New York didn't effectively reduce its heroin use rate or solve underlying problems such as poverty — the things that gun rights advocates often claim actually contribute to gun violence. But New York did tighten gun restrictions, which coincided with less violence.

"The proliferation of off-the-shelf handguns is really our problem," Pollack says. "If we regulated guns the way that England regulates guns, we would certainly have a much lower homicide rate."