And the firearm death rate in the United States is nearly 6.5 times higher than Canada's rate of just 0.5 per 100,000 people, the United Nations reports.
"Our peer countries regulate the guns . . . and they tend to have far lower homicide rates than we do," said Duke's Swanson.
Australia in 1996 enacted a gun buyback program in response to a massacre in Tasmania that left 35 dead. The result: Gun-related homicides declined from 0.57 per 100,000 people in 1996 to 0.1 per 100,000 people in 2009, according to GunPolicy.org.
In Japan, known for its restrictive gun-control laws, the total number of guns held by civilians is estimated to be 710,000, or 0.6 firearms per 100 people, according to data compiled by GunPolicy.org. In the United States, it's 270 million total guns, or 88.8 firearms per 100 people.
People who study violent behavior point to the widespread availability of guns in America, particularly assault weapons like the ones used in Newtown, Conn., that are designed to discharge multiple rounds of ammunition, as a factor in crimes involving multiple casualties.
"There just happens to be very lethal methods available out there," said Thomas Bowers, associate professor of psychology at Pennsylvania State University, Harrisburg.
Gun enthusiasts, however, argue that even the best gun control laws can't stop a person from committing a heinous act. Connecticut laws restricting the sale, ownership and use of guns are considered among the most stringent in the nation.
"None of these bans was efficacious in keeping Adam Lanza [the Newtown school shooter] from killing 20 children," said Michael Hammond, legislative counsel to the Gun Owners of America in Springfield, Va.
Police said Lanza used guns -- a semi-automatic rifle and two handguns -- that belonged to his mother, who was found dead in their home.
The National Rifle Association broke its silence on the Newtown tragedy on Wednesday with a statement explaining that "we have given time for mourning, prayer and a full investigation of the facts before commenting." The Washington, D.C.-based gun lobby announced plans for a "major news conference" on Friday.
Professing not to be a gun control fanatic, Christopher Ferguson, associate professor and chair of the department of psychology and communication at Texas A&M University in Laredo, believes gun access is part of the problem. "We may be getting to a point where we need to sit down and talk about what we can do to make things a little safer," he said.
The problem isn't just guns, experts say
Guns are only part of the equation, Ferguson said. There's also a need to improve the nation's mental health system so that individuals at risk get the help they need.
While no firm profile of school shooters has emerged, Ferguson said some common characteristics include a long history of anti-social traits, mental health problems such as depression or psychosis, and the perception that others are to blame for their problems, that "society didn't give me a chance."
A 2007 report commissioned by the U.S. Substance Abuse and Mental Health Services Administration found many gaps in the mental health system, "including a critical shortage of all child and adolescent providers," Dr. Howard Liu, medical director of the Behavioral Health Education Center of Nebraska at the University of Nebraska Medical Center in Omaha, told HealthDay.
In the report, the federal government projected a need for 12,624 child and adolescent psychiatrists by 2020, vastly exceeding the projected supply of 8,312. The shortage of trained mental health providers is particularly acute in rural and low-income areas.
Could the way Americans live and raise children today also play a role in triggering violent behavior?
Many people speculate that violent video games predispose kids to aggressive and dangerous behavior. Ferguson's research indicates that that's not true. In a laboratory setting, short-term exposure to violent videos neither increased nor decreased aggression, while long-term exposure was associated with reduced hostile feelings and depression following a stressful task, one study found.