Would the enhanced background checks it requires for those under 21 have stopped the suspect, Robert "Bobby" Crimo III, from buying the high-powered rifle authorities said he used -- since he'd had two prior run-ins with law enforcement, including both a suicide threat and one to "kill everyone" in his family?
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And could the law's red flag provisions have made a difference given that record and his apparent trail of violent social media posts?
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Evidence about the exact circumstances is still being revealed as the investigation gets underway.
But authorities said Crimo, now 21, purchased the high-powered rifle and other guns he had legally, passing numerous background checks. And because he did so in 2020 and 2021 -- when he was under 21 -- some advocates say the new law, which allows checks of juvenile and psychiatric records, might have made a difference.
At the same time, while Illinois has an existing red flag law, Crimo appears to have slipped past the safeguard.
Advocates say more education and training, provided for in the new federal law, is needed for a red flag law to be used effectively.
"We still need to learn more, but it looks like the shooter exhibited some dangerous warning signs, exactly what Illinois's red flag law is designed to address," John Feinblatt, president of Everytown for Gun Safety., told ABC News in a statement. "But tools are only useful when they are taken out of the toolbox and so far it doesn't look like anyone filed for an extreme risk protection order in this case. That's why the federal funding for red flag law implementation and awareness in the Bipartisan Safer Communities Act, combined with state action like lawmakers in Illinois are considering to prohibit the sale of possession of assault weapons and high capacity magazines, can make a big difference in preventing tragedies like the one in Highland Park."
What's in the new federal law
Gun violence experts said the $750 million allocated for red flag laws, also known as extreme risk protection orders, can be a critical tool for curbing these shootings.
"In my opinion, the federal funding that is now available for full implementation is exactly what this country needs to assure that extreme risk protection order laws are used to prevent the kinds of massacres that happened on the Fourth of July," Dr. Shannon Frattaroli, director of the Johns Hopkins Center for Injury Research and Policy, told ABC News.
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That money, Frattaroli explained, can go toward training law enforcement, judges and the community on how to use these laws to improve safety.
Illinois is one of 19 states with such a statute on the books, but Lake County State's Attorney Eric Rinehart said this week that they "must vastly increase awareness and education about this red flag law."
Enacted in 2019, the measure allows loved ones or law enforcement to intervene by petitioning a court for an order to temporarily prevent someone in crisis from accessing guns.
But Crimo seemingly eluded the law, as no arrests were made in either run-in with law enforcement. Highland Park police did notify Illinois State Police of the 2019 incident in which he allegedly threatened his family members in a "clear and present danger" report, but state police said their involvement in the matter ended because at the time Crimo did not have a FOID card or an application to deny.
EXPLAINED: Illinois' Clear and Present Danger Law vs. Firearms Restraining Order Law
ISP explain clear and present danger process
Three months later, Crimo did apply for a FOID card -- which is required for gun ownership -- and had his application sponsored by his father. State police approved the request in 2020, stating at the time "there was insufficient basis to establish a clear and present danger and deny the FOID application."
New information about Crimo's personal history is also raising questions about whether the enhanced background check portion of the Bipartisan Safer Communities Act could have applied.
Crimo just turned 21 last year, and purchased three guns in 2020 and one in 2021.
Under the new law, potential gun buyers under the age of 21 are placed under an investigative period to review juvenile and mental health records, including checks with state databases and local law enforcement.
Robin Lloyd, the managing director at the gun control group Giffords, said the enhanced background checks are designed to increase communication between different agencies.
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"The idea here is that there might be more information about that individual that exists in other places that the background check doesn't check under current law," she said, "and it also gives an opportunity to contact local law enforcement."
But Lloyd said there is more work to be done in order to curb gun violence.
"The holistic picture is that we have very weak federal gun laws," she told ABC News.
While Illinois has the eighth-strongest gun laws in the nation, according to Giffords, Lloyd noted that neighboring states have less restrictions and firearms can easily move across borders.
"So while the Bipartisan Safer Communities Act is a very significant step forward in terms of federal gun safety policy, it is not the only thing that needs to be done," Lloyd said. "It is not going to prevent every shooting from happening."
What lawmakers are proposing next
In the wake of the shooting, some lawmakers are once again calling for stronger legislation that would ban the sale, transfer, manufacture and importation of military-style assault weapons, ban certain high-capacity magazines, and enact universal background checks.
"There are things we can do," Rep. Brad Schneider, an Illinois Democrat whose district includes Highland Park, told ABC News on "GMA3."
"The House has passed legislation to require universal background checks. Ninety percent of the country supports that legislation," Schneider said. "We need to pass it and make it law. We can ban the sale of these assault weapons, make it harder for people to get the large capacity magazines that allow them to fire off 60 rounds in just a matter of seconds."
Vice President Kamala Harris also made an impassioned plea for an assault weapons ban during a visit to Chicago on Tuesday.
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"An assault weapon is designed to kill a lot of human beings quickly. There is no reason that we have weapons of war on the streets of America. We need reasonable gun safety laws," Harris said as she addressed the National Education Association. After that meeting, Harris visited the Highland Park shooting scene.
But any additional gun restrictions will face an uphill battle in the Senate, where Democrats need 10 Republican votes to clear the filibuster.
Republicans responded to Monday's shooting by continuing to blame mental health issues rather than access to assault weapons.
Republican Sen. Mitch McConnell, who backed the Bipartisan Safer Communities Act, said Tuesday that the "problem is mental health and these young men who seem to be inspired to commit these atrocities."
Democrats are encouraging voters ahead of the 2022 midterm elections to support candidates who back stronger gun control.
"It's not going to happen tomorrow," said Democratic Sen. Dick Durbin of Illinois. "It's going to happen when the American people speak up and elect those who really want to make a change that'll make America safer."