The suspect in the shooting that killed 10 people at a grocery store in Boulder, Colorado, on Monday used an "AR-style rifle," local law enforcement have said. It's a comparatively lightweight and portable semi-automatic weapon popular with police and mass shooters. It's also a style the City of Boulder banned two years ago, amending municipal gun regulations to expand the definition of illegal weapons in light of past mass shootings nationwide. But 10 days before this attack, the ban's enforcement was suspended by a court ruling. Did that decision make these awful murders possible?

The law's supporters suggest it did. "We tried to protect our city," one Colorado gun control advocate told The Washington Post. "It's so tragic to see the legislation struck down, and days later, to have our city experience exactly what we were trying to prevent."

I'm not so sure it would have made a difference, and I mean that both in terms of the specific city ordinance and in regards to how gun control tends to function more generally.

Any person who "was legally in possession of an assault weapon" prior to the ban had four options, the Boulder ordinance said: They could remove it from the city, render it inoperable, surrender it to police for destruction, or apply for a permit before the end of 2018. For those who chose the latter option, there were five requirements: Undergo a background check, apply for the permit from the Boulder police, secure the weapon, limit its secure storage to a few select locations (the owner's home, repair shops, licensed gun ranges, and the like), and agree to promptly file a police report if it's stolen. Anyone who didn't comply would have their weapon confiscated and could be fined or jailed.

Little information about the suspect in Boulder has been released as of this writing, but an affidavit published Tuesday says investigators used "law enforcement databases" to discover he "purchased a Ruger AR556 pistol on March 16, 2021." It also lists his address as Arvada, Colorado, which is in the Denver metro area south of Boulder.

That residency detail means the ordinance and the court ruling are almost certainly irrelevant to this case. Boulder's gun law couldn't have kept the suspect from buying this gun if he lived outside Boulder. Moreover, if he had a legally obtained weapon appropriately secured in his private vehicle, he was allowed to drive through Boulder with it in his car. He was also allowed to stop at the grocery store. The ordinance specifically permits that kind of transport, "regardless of the number of times the person stops in the City of Boulder."

What if the suspect did live in Boulder? We're speaking hypothetically now, but it's possible (albeit improbable) a Boulder resident could have found a gun shop within city limits that had restocked AR-style guns in the 10 days immediately after the court decision. The timeline's awfully tight by the time you add in the background checks Colorado requires for most gun transfers. But yes, it's possible the ordinance would have made a difference in that counterfactual scenario.

Yet speaking of counterfactuals, here's another: If the suspect lived in Boulder and had already acquired the gun when the ordinance went into effect in 2018, he probably would've been allowed to keep it. We know he was convicted of misdemeanor assault three years ago, but the federal and Colorado laws cited in the Boulder ordinance's background check provision specify domestic violence as the only misdemeanor violation that can keep you from getting a weapon. In this hypothetical, the suspect likely would've passed the background check and kept his gun. Indeed, the fact that the police consulted law enforcement databases to find the purchase record suggests he did pass a background check this very month. If that's true, instituting universal background checks, a widely popular gun control proposal, wouldn't have changed anything here.

Having run through all these possibilities, I can anticipate the rejoinder from those who want stricter gun laws: We need to bring back the Boulder ordinance with the grandfather clause eliminated — or expand it to the state level so someone from Arvada couldn't shoot people in Boulder — or, ideally, take it nationwide, so a would-be shooter would have no legal way to obtain an AR-style gun in the United States.

I don't think we know enough about this suspect so far to speculate whether a national ban could have forestalled him. It would forestall some people. It would inconvenience them enough that they would choose a less deadly but more accessible weapon — another gun or a knife or vehicle — or even forego their rampage altogether. That marginal effect would be real.

The open question is the size of the margin. How many potential attackers would be deterred or forced to alter their plans, and how many would simply acquire AR-style guns illegally? The Boulder ordinance includes exceptions for law enforcement and the military, as would a national ban, which means we'd still have plenty of these guns in our country. They could be stolen. Guns could also be smuggled in and sold on the black market. Mass shooters are not big rule-followers.

I suspect the margin is bigger than gun rights advocates believe. With a national ban on AR-style weapons, we might well see fewer mass attacks and a lower average casualty count in the attacks that aren't prevented.

But I also suspect the margin is quite a bit smaller than the gun control crowd expects. Gun prohibition has many of the same problems as drug prohibition: Legal distinctions are frequently arbitrary. Enforcement is difficult and often ineffective and/or discriminatory toward marginalized populations. It's used to justify invasive surveillance and an entrance point for the government to meddle in private lives. It can enormously expand the police and carceral states, too. New Jersey banned unregistered assault weapons in 1991, and just four of as many as 300,000 guns were surrendered in the first year, even on threat of felony prosecution. There are around 15 to 20 million of these weapons in America today. Many are unregistered. How exactly would the government collect them?

After every mass shooting, we ask ourselves if there were some way to prevent it. In Boulder, the answer looks like "no" where that city ordinance is concerned. For future attacks, could it be "yes" with a more aggressive — and riskier — national AR-style gun ban? We may soon test the theory.