SALT LAKE CITY (AP) — For the second time in less than a week, a 21-year-old man used a gun purchased legally in the United States to massacre people simply working or visiting a business. The mass shootings in Colorado and Georgia are giving new urgency to state efforts to enact gun restrictions, even while showing how hard it can be to prevent a tragedy.

A gunman opened fire Monday at a grocery store in Boulder, Colorado, with a weapon that resembles an AR-15 rifle, killing 10 people before he was captured. He bought the Ruger AR-556 pistol on March 16, the same day another 21-year-old man on the other side of the country killed eight people, six of them women of Asian descent, at Atlanta-area massage businesses.

President Joe Biden called for action on gun reform after the two mass shootings, and U.S. Rep. Joe Neguse, who represents Boulder, asked Biden to ban imported semi-automatic weapons and high-capacity magazines. But legislation in Congress faces an uphill climb, and it’s been more than two decades since any major federal gun control laws have passed.

That means most significant gun legislation has been left to the states, including Colorado, where lawmakers have passed gun control laws in recent years. But the suspect in the supermarket shooting, Ahmad Al Aliwi Alissa, still could legally buy a firearm, keep it despite concerns about his mental state and open fire in a town that had tried to ban assault-style weapons.

That’s led to calls for stronger action from the state, and Democratic leaders are listening. Still, support for gun rights is strong in parts of Colorado, and Second Amendment advocates argue new restrictions are not the answer.

Colorado has a law requiring background checks on almost all gun sales. The suspect had a misdemeanor assault conviction from high school, but it didn't prevent him from buying a gun from a shop near his suburban Denver home because most misdemeanors don’t block people from legal firearm purchases.

The state also has a so-called red flag law that allows families to ask a judge to remove guns from people who could be dangerous. Alissa's family had concerns about his mental health and a sister-in-law had seen him with the weapon, police said.

But the law requires evidence that a person poses a significant risk in the near future. It’s unclear whether anyone close to him was concerned enough to begin the court process in the six days between the gun purchase and the shooting, but general concerns about someone’s behavior aren’t typically enough to persuade a judge to order that weapons to be removed, said Jacob Charles, executive director of the Firearms Law Center at Duke University.

Meanwhile, a ordinance in the city of Boulder that banned assault-style weapons was struck down in court just days before the shooting because of a state law that bars local leaders from making their own gun rules. Now, state Senate Majority Leader Stephen Fenberg is drafting a bill to repeal that law. It could also be paired with other new legislation.

“There’s not one answer to this problem. It has to be a complex and comprehensive set of policies because every tragedy is different,” he said.

David Kopel with the libertarian think tank Independence Institute in Colorado questioned the effort to repeal the law. Allowing communities to pass their own rules could mean that law-abiding gun owners have a patchwork of rules to follow in every town they drive through, he said.

“Almost all law ultimately depends on voluntary compliance. You get more compliance when you have a uniform set of laws that everyone can know,” Kopel said.

Some Colorado communities want to go the other way and have looser gun laws than those at the state level, he said.

Instead of passing new laws, Kopel argued, the state should increase funding for mental health treatment. In Alissa's case, authorities have said his family was concerned about his mental health and defense attorneys are asking for an evaluation.

To keep guns away from people in crisis, gun control activists say Colorado should create a waiting period. Both Colorado and Georgia, like the majority of states, allow people to get a gun right away. In the Atlanta area, the shooting happened just hours after the purchase.

Supporters say a waiting period could allow time for people to cool off if they’re considering hurting themselves or others, though Kopel argued it would also unfairly affect gun-show sales.

Waiting-period legislation is already in the works in Colorado, and Georgia Democrats plan to introduce a measure that would require people to wait five days between buying a gun and getting it, state Rep. David Wilkerson has said. And with gun sales nationwide having surged to record levels last year amid pandemic-related uncertainty, lawmakers in at least four other states have proposed creating or expanding waiting periods.

Boulder community activist Caden McGhie, a 21-year-old college student, supported the idea in Colorado. Growing up after the 1999 Columbine High School massacre, he had nightmares from active shooter drills at school.

“The real goal in all of this is to show people there is something you can do. You’re not entirely powerless,” McGhie said. “While this is absolutely terrifying ... we can make a difference, and we can make it now, and hopefully we can make it before something else happens.”

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Patty Nieberg, a corps member for the Associated Press/Report for America Statehouse News Initiative, contributed to this story. Report for America is a nonprofit national service program that places journalists in local newsrooms to report on undercovered issues.