"Jesse was the love of my life," Neil Heslin, father of Jesse, told a panel of senators as he held up a framed photo of himself and his only child as spectators at the hearing openly wept. "He was the only family I had left."
Heslin, a 50-year-old construction worker, dismissed arguments by gun control foes that banning assault weapons violates the U.S. Constitution's Second Amendment right to bear arms.
"When it was written almost 300 years ago, we didn't have these weapons that we have today; they had muskets and cannons," he said.
Assault rifles, on the other hand, have no place in the hands of civilians given they "were used in a battlefield in Vietnam. They were used in the Persian Gulf, they were used in Afghanistan, in Iraq. The sole purpose is to put a lot of lead on a battlefield quickly."
Jesse was one of 19 first grade pupils gunned down in Newton, Conn., in December by a troubled young man toting his mother's assault rifles. Six adults also died in Adam Lanza's rampage, including his mother as she lay in bed.
The latest mass shooting to horrify Americans, however, has served as a tipping point, with a measurable shift in public attitude in favour of tougher gun control laws in a nation with the highest rate of firearms ownership in the world.
In the aftermath of Newton's bloody carnage, polls now suggest the majority of Americans support both an assault weapons ban and universal background checks.
The new zeitgeist wasn't readily apparent at Wednesday's Senate hearings, however, when the Republicans on the panel and some of the witnesses argued against a ban. The powerful National Rifle Association, which receives funding from gun manufacturers, in turn contributes to the campaigns of several Republican legislators, and some Democrats in gun-friendly states too.
Democratic Sen. Dianne Feinstein, the chairwoman of the Senate's judiciary committee, has introduced a bill in the upper chamber that would ban assault weapons and high-capacity ammunition magazines.
The proposed legislation is part of President Barack Obama's push for tougher gun control laws in the wake of Newtown. The Senate committee is slated to consider several gun bills as early as Thursday.
The hearing frequently grew heated between those for and against Feinstein's bill. Nonetheless, when applause broke out among spectators — unusual during a Senate hearing — each time it was in response to those arguing in favour of tougher gun control laws.
Edward Flynn, the police chief of Milwaukee, was particularly passionate as he argued with Sen. Lindsey Graham of South Carolina, who accused law enforcement of neglecting to prosecute those who fail existing background checks.
Republicans argue that more diligent enforcement of existing laws makes more sense than imposing new ones.
"We don't chase paper, senator, we chase armed criminals," Flynn snapped as spectators whooped and applauded.
Flynn also alleged that opposition to gun control is often fuelled by "commerce," not concerns for public safety, noting the gun business in the U.S. is a multi-billion-dollar industry.
In his remarks to the hearing, Graham frequently spoke of hypothetical situations in which civilians would need assault rifles to fend off "gangs of armed criminals."
Democratic Sen. Al Franken urged his fellow lawmakers to deal in reality, not in fantasy.
"I can imagine those hypothetical cases but I'm not sure what value that holds," he said. "But I don't have to imagine someone using a 30-round magazine, or several, to kill 20 children, because that happened."
Another witness, U.S. attorney John Walsh of Colorado, said he had found no evidence of civilians using assault rifles for self-defence.
Feinstein's bill would outlaw about 160 different types of military-style assault weapons. But it has almost no hope of being signed into law given Senate Democrats lack the 60 votes needed to thwart a Republican filibuster on the bill.
The California senator helped craft legislation in 1994 to ban assault weapons. It expired 10 years later, but gun control advocates cite a 2004 study that indicated gun crime diminished by as much as 72 per cent throughout that decade.
Gun control foes, meantime, point to data in the same study that showed assault weapons were used in only two to eight per cent of gun crime, arguing that an assault weapons ban would therefore have scant impact.
The NRA tweeted throughout the Senate hearing on Wednesday, including one curious dispatch that appeared to boast that in the first hour of testimony, Americans had bought an additional 150 AR-15s, the assault weapon used in several mass shootings.
Dick Durbin, a Democratic senator on the committee, chided one anti-gun control witness who dismissed Feinstein's bill as "feel-good" legislation shortly after Heslin and William Begg, the head of emergency services for Newtown who tended to some of the bullet-ridden victims, delivered their emotional testimony.
Sandy Adams, a former Republican congresswoman from Florida, said now was not the time for "feel-good legislation so you can say you did something."
"Taking guns from law-abiding citizens while leaving them defenceless against violent criminals, who by their very definition do not abide by the law, is not the answer and it is definitely not the right thing to do," she said in her opening statement.
Durbin rebuked her, and shook his head when she told him she also opposed universal background checks.
"I don't feel good about being here today," he said scathingly. "Mr. Heslin does not feel good about being here today."
He added to applause: "What has become common in America is unacceptable in a civilized country."
Another witness, Philadelphia Mayor Michael Nutter, scolded Republican senators and anti-gun control witnesses, saying they'd been "dispassionately disrespectful" to Heslin and other victims' families in attendance at the hearing.
That remark too was greeted with applause, as was his insistence that no one has ever been able to explain to him why civilians need assault weapons.