Washington (CNN) -- Newtown. Aurora. Columbine. Tucson. Virginia Tech.
The tragic shootings in each of these and other towns have ignited public sentiment for some kind of gun reforms and fired up gun advocates to protect what they see as their constitutional right of easy access to firearms.
According to recent polls, more than 90% of Americans favor some form of background checks for firearm purchases, particularly at gun shows, but the efficacy of the measure remains dubious by both law enforcement and gun control advocates.
But, as Congress wrestles with what new measures -- if any -- should be passed to control gun purchases, one question looms:
In those and other mass shootings, would background checks have made any difference?
Looking back, background checks did not stop three mass shootings that claimed more than 40 lives since 2011.
In the massacre in Newtown, Connecticut, where 26 people, mostly children, were gunned down at Sandy Hook Elementary School, Adam Lanza used two semi-automatic handguns and a semi-automatic rifle. He didn't get a background check for those weapons. They were legally purchased and registered to his mother, Nancy Lanza, who was his first victim.
Last July, James Holmes walked into a crowded theater in Aurora, Colorado, and began shooting. His AR-15, two 9 mm Glocks, .40 caliber pistol and 12-guage shotgun were all purchased legally, after his name was submitted to the National Instant Criminal Background Check System (NICS). Twelve people were killed.
The same is true with Jared Loughner, who shot then-Rep. Gabrielle Giffords and 19 other people, killing six, in Tucson in January 2011. His application was never flagged when run through NICS -- the database from which potential firearms buyers are determined legally eligible to purchase a gun.
"The one shooter that might have been prevented by background checks and was not was the Virginia Tech shooter because he had, in fact, been adjudicated to be potentially violent," said National Rifle Association President David Keene.
Seung-Hui Cho, who killed 32 people in 2007 on the picturesque Virginia Tech campus in Blacksburg, had been deemed mentally ill by a judge, which is one of the criteria used to disqualify certain people trying to buy a gun. Others who could be potentially disqualified include convicted felons, fugitives, drug addicts and domestic abusers.
Cho's case apparently slipped through the cracks and the state of Virginia has since instituted a series of reforms in its reporting procedures to NICS as a result.
Cho might have been stopped if universal checks were the law, Vice President Joe Biden said.
"One of the problems that was pointed out here was that there was an adjudication of the young man that committed the crime at Virginia Tech, and yet he was able to go out and purchase two weapons," Biden said in January.
The current Senate proposed bill called the "Fix Gun Checks Act" seeks to remedy the database deficiencies by forcing the states to become more involved in submitting names into the existing system.
The sticking point with the proposal for many anti-gun control proponents is the requirement that background checks cover every firearm sold, whether at gun shows, the Internet or private sales.
Sens. Joe Manchin III, D-West Virginia, and Patrick J. Toomey, R-Pennsylvania, announced Wednesday a bipartisan deal on background checks for gun shows and Internet sales, but a similar agreement in the House is still unlikely.
Sen. Chuck Schumer, D-New York, who wrote the latest Senate bill, said his was an expansion of the 1994 Brady Handgun Violence Prevention Act that banned military-style assault weapons for a decade before it expired.
"Every major expert believes that universal background checks will save lots of lives," Schumer told CNN.
He added that 1.7 million people "have gone to firearms dealers and been denied guns because they were felons or adjudicated mentally ill because of the Brady law."
But the NRA's Keene disagreed.
"The tipping point for all this gun control talk about background checks is actually an example of how background checks don't matter... [the] killer will find a way to get a gun even if he kills the owner."