The massacre of 10 people at a Boulder supermarket occurred under a confusing mix of local, state and federal gun laws -- but no Colorado statute prohibiting a person with mental illness from owning firearms.
The suspect, Ahmad Al Aliwi Alissa, purchased a semiautomatic pistol six days before Monday's shooting, according to his arrest warrant affidavit. His brother told CNN he believes Alissa was "antisocial" and living with a mental illness, but it's unclear whether the suspect had been diagnosed.
Under federal law, anyone who has been involuntarily committed to a mental health institution or determined by a lawful authority as a danger to others as a result of a mental illness is banned from owning a firearm.
Most states use different definitions for mental illness, creating a nationwide patchwork of laws. To complicate matters further, some state laws vary from the federal law.
One criminal justice expert believes these inconsistencies create confusion.
"We really need an across-the-board, all-50-states law that specifically states what we are talking about and covers everybody," said Joseph J. Vince, a former special agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives.
"An umbrella law works better than a hodgepodge of laws because people travel and they can go to different states," he added. "People (under an umbrella law) would understand specifically what we're enforcing."
Differences between state and federal laws can create loopholes
Colorado is one of four states, along with Indiana, Kentucky and New Hampshire, that rely on the federal umbrella firearm law and don't have a specific state law banning firearm possession by people with a mental illness, according to the National Conference of State Legislatures.
For federal law to be effective, states have to be compliant and transparent, said Vince, who teaches criminal justice at Mount St. Mary's University in Emmitsburg, Maryland.
Discrepancies between federal and state law can create legal loopholes, he said.
For example, the gunman who killed 32 people at Virginia Tech in 2007 had been declared mentally ill by a court and ordered to undergo mental health treatment. Under federal law, that should have disqualified him from owning a gun.
But he was able to buy a gun because his treatment was outpatient, and at the time, Virginia state law only disqualified a person if they had been involuntarily committed to a mental hospital. As a result, Virginia never reported him, and he was not flagged in a background check.
States are currently supposed to send information on weapons buyers to the National Instant Criminal Background Check System (NICS) but there's no mandatory requirement, which creates a gap in communication, Vince said.
Then there's a timing issue. When someone tries to buy a firearm, the seller contacts the NICS, which performs a background check. The NICS must verify a buyer's eligibility within three business days. If it can't resolve the issue within three days, the dealer has the right to sell the firearm unless its prohibited by the state, Vince said.
The US Supreme Court ruled in 1997 that Congress could not compel states to report prohibited persons to the NICS. As a result reporting is uneven and in some states, inpatients with serious mental illness are never even entered, said James Densley, co-founder of the Violence Project, a nonpartisan research center dedicated to reducing violence in society.
The federal law governing access to guns by people with mental health problems was passed in 1968 and has not kept up with changing times as many Americans buy weapons online, Vince said.
"It would be extremely difficult to keep track of everyone, but we have to do a better job of examining who acquires weapons," he said.
Colorado's 'red flag' law allows courts to take guns away from people seen as a danger
Colorado has a number of gun-control laws, including universal background checks and a ban on high-capacity ammunition -- magazines that hold more than 15 rounds.
It also has a newer "red flag" law, effective January 1, 2020, that allows a judge to temporarily remove weapons from people considered a threat to themselves or others.
A handful of states have red flag laws to take firearms from people deemed to be dangerous. Vince, the former ATF agent, says such laws are better at intervention than prevention. The goal is to stop crimes before they happen, he said.
"The red flag law allows law enforcement to intervene when someone is known to have a gun and is in a moment of crisis," Colorado State Senate Majority Leader Steve Fenberg told CNN this week.
"But there's more that we need to do clearly," he added. "I don't think you'll ever get to a place where you end gun violence. But it doesn't mean that you shouldn't strive to get there and make improvements. And every improvement you make may prevent the next crisis."
Alissa, the suspect in the Boulder shooting, bought a Ruger AR556 pistol on March 16, according to an arrest affidavit. It was not immediately known where the gun was purchased.
Four days earlier, a state district judge had blocked a ban on assault rifles that was passed by the city of Boulder in 2018, citing a Colorado law that prohibits a local government from imposing weapons measures that contradict state or federal law.
If Alissa had purchased the gun in Boulder and that law had been in effect, it would have prevented him from buying it, Fenberg said. "No question, that weapon wouldn't have been able to be purchased within city limits," he said. "It would have been illegal to possess that type of weapon."
People with a mental illness are more likely to be victims, psychiatrists say
Responding to mass shootings, the American Psychiatric Association said in 2019 that linking mental health and violence risks stigmatizing people who need treatment. Those with mental illness are more likely to be victims of violent crime than offenders, it said.
Mass shootings by people with serious mental illness make up less than 1% of all gun-related homicides, said Dr. Jeffrey Geller, president of the American Psychiatric Association. In contrast, deaths by suicide using firearms account for the majority of yearly gun-related deaths.
"The overwhelming majority of people with mental illness are not violent and much more likely to be victims of violent crime than perpetrators," Geller told CNN. "Linking mental health and violence will further stigmatize and interfere with people who might otherwise access needed treatment."
For that reason some might say federal restrictions are too broad, Densley said, because banning gun ownership for life after someone is hospitalized could increase stigmas and reduce reporting. "It's a sensitive balance," he said.
CNN's Konstantin Toropin contributed to this report