Trent Brewer drove to a parking lot, planning to sell some weed. The transaction never happened.

Police in Springfield, Mo., found Brewer, 23, face-down in a pool of his own blood with no pulse on Dec. 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, Colo., that her ex-boyfriend had kidnapped her, threatened her and threw her into a car dashboard. It was Saturday, Dec. 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-Calif., 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.

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, Mo., 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."