"Violence is a big problem," Giffords said, pausing between words she read from a hand-scrawled note. "Too many people are dying; too many children. We must do something. It will be hard but the time is now."
Giffords said lawmakers "must act. Americans are counting on you."
The hearing is the first to be held after the December massacre at Sandy Hook Elementary in Newtown, Conn., where authorities say a mentally ill man killed 20 children and six educators and his mother before shooting himself. The tragedy prompted the National Rifle Association and gun-rights advocates to call for armed security at schools nationwide.
Kopel, research director at the Denver University Independence Institute, said that gun opponents always come up with "all kinds of fantastic scenarios" about how guns in schools would lead to teachers shooting each other or threatening students, or that the students will steal the guns.
"But we've had this policy in practice in Utah for many years, and we've never had been a single problem," Kopel said. "And, quite notably, we've never had an attack on a Utah school."
Utah law specifically says a concealed firearm permit holder can carry a loaded and hidden gun into public schools.
Gary Sackett, a member of the board of directors of the Gun Violence Prevention Center of Utah, said Kopel may be correct that there haven't been any recent shootings in Utah schools but that it's an "empty argument" to say that's because of teachers with concealed weapons.
"No, we haven't had any mass shootings here but I don't think you can attribute it to people with handguns stuffed in their skirts or pants," Sackett said. "You could have said that very same thing up until a month ago in Newtown, Connecticut."
The NRA's chief executive officer, Wayne LaPierre, didn't mention Utah's law during his comments, though he continued to press for more armed guards in schools.
"It's time to throw an immediate blanket of security around our children," LaPierre said. "About a third of our schools have armed security already because it works."
Utah Republican Sens. Orrin Hatch and Mike Lee, both of whom serve on the Judiciary Committee, lobbed easy questions at the pro-gun rights witnesses, paralleling their talking points against the idea of restricting high-capacity firearm magazines and expanded background checks.
"What about criminals, those who use weapons like these in connection with crimes? Do you think they are as likely to abide by that law?" Lee asked a woman representing a conservative think tank and referring to a proposal to limit the capacity of gun magazines.
"By definition, criminals are not abiding by the law," responded Gayle Trotter, an attorney with the Independent Women's Forum.
Wednesday's hearing, which highlighted the polarization over gun rights, was arguably the most packed congressional event since the controversial health care meetings in 2009. Scores of people waited in long lines in hopes of grabbing a seat, while Chairman Patrick Leahy occasionally slammed down his gavel to quiet audience laughter or shouts.
While Giffords made a short statement and was helped out of the room, her husband, former astronaut Mark Kelly, made a passionate plea for taking action to keep firearms out of the hands of dangerous people and to limit magazines to less than 10 rounds.
Kelly, who said he and his wife own guns and won't relinquish them, noted that in the attack where Giffords was shot, more lives were saved because the gunman dropped his magazine while trying to reload and was tackled by civilians.
"When dangerous people get dangerous guns, we are all the more vulnerable," Kelly testified. "Dangerous people with weapons specifically designed to inflict maximum lethality upon others have turned every corner of our society into places of carnage and gross human loss."