(CNN) -- Trent Brewer drove to a parking lot, planning to sell some weed. The transaction never happened.
Police in Springfield, Missouri, found Brewer, 23, face-down in a pool of his own blood with no pulse on December 12. He was declared dead at a nearby hospital.
Police say Darian Earl Hall, 18, pulled out a chrome semi-automatic handgun before the sale could happen, and opened fire on Brewer as he began to run away.
Hall has denied shooting Brewer, blaming another teen who was with him at the time. What exactly happened will eventually be settled in court.
Brewer's story follows a familiar pattern: drugs, an escalating confrontation and the presence of a gun leading to a death.
Beatriz Cintora-Silva took refuge at her sister's home immediately after telling police in Longmont, Colorado, that her ex-boyfriend had kidnapped her, threatened her and threw her into a car dashboard. It was Saturday, December 16.
The next day, police arrested Daniel Sanchez, 31, who spent Sunday night in jail.
Six hours after Sanchez left the Boulder County jail, a call came into 911:
"No, no, no, please, no," Cintora-Silva said on the call.
Gunfire rang out and the phone went silent.
Then, Sanchez picked up the phone.
"I just shot everyone right now," he said, according to a recording of the 911 call.
"You just shot everybody?" the dispatcher asked. Sanchez calmly replied "Yeah."
She asked for his name, but he didn't answer.
"I'm going to shoot myself right now," Sanchez said on the recording. The dispatcher pleaded with him.
It didn't matter. The line went dead.
Sanchez had shot and killed Cintora-Silva, her sister and her sister's husband before killing himself with one of the most deadly weapons in the United States.
It wasn't an AR-15, or an assault rifle -- it was a Glock .45-caliber handgun.
America's most deadly firearm
Trent Brewer and Beatriz Cintora-Silva are among the more than 6,000 people killed each year by handguns.
That's like having a massacre on the scale of Newtown 239 times during one year.
Yet, as the Obama administration moves forward with legislation to stem the toll of gun violence in America, the focus has been on curbing access to high-powered rifles and large-capacity magazines, not the common handguns that account for the majority of gun deaths in America.
Last week, Sen. Dianne Feinstein, D-California, stood in front of an array of assault rifles and semi-automatic weapons and outlined her proposed legislation to reinstitute an assault weapons ban, as well as outlaw ammunition magazines that hold more than 10 rounds.
The graph below details gun-related homicides in 2011 by weapon type. This breakdown has remained consistent across the most recent five years of data made available by the FBI.
Source: FBI Criminal Justice Information Services
But even if these proposals make it through to legislation, what impact will they have on stemming the deaths by America's most deadly firearm?
Despite the National Rifle Association's assertion that Feinstein and other Democrats are taking steps toward outlawing all guns, no lawmaker is calling for a ban on the legal purchase of handguns. These common firearms, which account for the majority of gun-related violence in America but are also used for self-defense, are fully protected by the Second Amendment, according to a 2008 Supreme Court ruling.
Speaking Monday before a meeting with police chiefs and sheriffs from across the country, Obama said he understands that America's gun violence problem runs deeper than the mass shootings that trigger international headlines.
"I welcome this opportunity to work with (law enforcement), to hear their views in terms of what will make the biggest difference to prevent something like Newtown or Oak Creek from happening again," the president said. "But many of them also recognize that it's not only the high-profile mass shootings that are of concern here, it's also what happens on a day-in-day-out basis in places like Chicago or Philadelphia, where young people are victims of gun violence every single day."
There are three main ways that Obama's plan could indirectly stem the toll of handgun violence:
• increasing access to mental health services
• lifting restrictions on federally funded research on gun violence
• extending background checks before the purchase of a gun
It's unclear if any of these proposals would have affected the outcome of the Springfield, Missouri, drug deal that claimed the life of 23-year-old Trent Brewer.
But in domestic violence incidents, like the one that killed Beatriz Cintora-Silva, even something as simple as considering an accuser's mental state could make a difference, according to CNN's mental health expert Dr. Charles Raison.
For example, if police detained accused abusers for a longer time, would that allow for a cooling off period and a decreased chance of violence?
"The only way to interrupt (violent incidents) is to lock up and intervene tons and tons of times, where everyone who exhibits symptoms is locked up," said Raison, an associate professor of psychiatry at the University of Arizona in Tucson. "But then as a society, where do we want to strike a balance between personal freedom and intervening to stop the high rate of violent acts?"
Despite all his concerns, Raison said he finds the discussion about opening up access to mental health services promising, but also "an extremely slippery slope."
According to the FBI, 6,220 people were killed by handguns in 2011 and many law enforcement and public health experts say that shows much more needs to be done to seriously address the gun violence epidemic -- even more than what the president or Congress proposes.
"These are all steps in the right direction to keep guns out of the hands of people who shouldn't have them, the mental health issues, those are all good things," said Mike Bouchard, a retired agent with the Bureau of Alcohol Tobacco and Firearms and president of Security Dynamics Group, a consulting firm that ensures companies are compliant with firearm regulations.
"But I don't know that it's going to reduce the homicide rate."
Searching for answers
Trent Brewer and Beatriz Cintora-Silva were part of a fairly typical pattern of homicides in December 2012, the same month as the Newtown mass murders.
Exactly how many others across the United States met the same fate that month?
There's really no way to know. That's because of a lack of data. The FBI details homicides each year but it often has a lag time in reporting and does not specify the exact type of weapon. While the CDC has a National Violent Death Reporting System to collect data for violence prevention research, it is only operational in 18 states.
A slew of researchers, professors and experts successfully urged Vice President Joe Biden to include researching gun violence as one of the proposals he submitted to the president. Biden led the gun violence task force created by Obama in the wake of last month's Newtown shootings.
Harold Pollack, co-director of the Chicago Crime Lab and one of the researchers who penned the recommendations to Biden, said he hopes this federal action will reverse the stifling of research and data since the 1990s.
That's when the powerful pro-gun National Rifle Association effectively ended federal funding for gun violence research, citing its opposition to taxpayer-funded studies on gun violence.
That type of research is exactly what Pollack said can eventually prevent some of the senseless deaths as a result of guns.
"If you look at 'How did someone get that gun that led to that person getting killed?' we might be able to find ways to have interfered with it," Pollack said. "Maybe it's related to the gun dealer, maybe it's a type of gun commerce that we can interrupt, or maybe there's a social service intervention before any of that."
He noted that studies of infant deaths and car accidents led to decreased rates of deaths in both cases.
Traffic accident research led to the discovery that many deaths were the result of impacts inside the car, not the car hitting a tree, for example.
That, Pollack said, is why we have airbags and seat belts. Those lifesaving additions to cars were a direct result of the tedious research.
That is how guns should be addressed, he said.
"We have to be able to use the tools that we have ... to try and make sensible policy," Pollack said. "If our data about critical matters is left in a dusty box of a basement in a courthouse, there isn't a whole lot we can do."
Obama has ordered the Centers for Disease Control and Prevention and other federal agencies to immediately begin research on gun violence, its impact and any prevention measures.
There is only one hurdle standing in the way: Congress has to give them funding.
Tracing gun sales
It can takes weeks or even months, if law enforcement is lucky, to trace a gun back to its origin.
Because many states don't require guns to be registered, or private sales to be documented, no one really knows who owns many of the guns in circulation in the United States.
That means authorities are often unable to find out how criminals got their guns.
While most people assume, perhaps because of TV shows or movies, that authorities can plug in a serial number and gather all the data about a gun, Mike Bouchard said that actually couldn't be further from the truth.
Bouchard, who works with firearm dealers to make sure they are compliant with the law, likens the situation to underage drinking: If someone can't get a beer, they may find someone who can buy it for them. The same is true of guns, he said.
"The rules are easily defeated," he said. "If (criminals) want a gun they are going to get a gun."
That's a hole that President Obama hopes to address with universal background checks, stronger control of gun sales and laws that would make it a crime to sell your own gun to someone without a background check.
Universal background checks would mark an important turning point in stemming gun violence, according to gun control advocate Lindsay Nichols.
"This may be the single most important gun violence prevention measure that the government could adopt," said Nichols, an attorney with the Law Center to Prevent Gun Violence. She said it would close a loophole that gave "dangerous criminals and dangerously mentally ill individuals ... a most unfettered access to firearms."
But NRA president David Keene suggested to CNN's Candy Crowley that he has little faith in universal background checks, saying they don't work.
That's because, Bouchard said, it assumes criminals will follow the law.
"These criminals don't care what the law says," he said.
While he said he believes expanding background checks is a step in the right direction, Bouchard said the real solution would be creating a database that tracks weapons purchases.
"If people knew every transaction of a gun was going to be recorded somewhere, I think they'd be more responsible with who they transferred their weapon to," he said.
Based on his experience, Bouchard said it would be pretty easy to establish a database to track weapon purchases and sales on a national level.
But he admits he doesn't know anyone who supports a nationwide gun registration.
Experts know that reducing the number of Americans killed by guns isn't a problem that will be solved overnight, let alone in a few years. It may take a long-term game of trial and error.
But with 12,000 to 15,000 people being killed by guns each year, Bouchard said the country has to start somewhere. Anywhere.
"Our whole society controls how much you can drink, how many pills you can buy, we have controls we accept on everything else in this society -- except guns," Bouchard said. "Those things are all acceptable to us. But with guns most people will not even discuss restrictions."
CNN's Emily Smith contributed to this report
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