California has strict gun laws. Here's how the Gilroy gunman evaded them

California has some of the most stringent gun laws in the country, including a ban on the type of rifle that a shooter used to kill three and wound 15 at the garlic food festival in Gilroy on Sunday.

But the gunman had legally purchased the “assault-type rifle”, in the style of an AK-47, from the neighboring state Nevada on 9 July before carrying it illegally over state lines into California, highlighting what some gun control advocates say is a loophole in the way laws operate, state by state.

The suspect, 19, opened fire in the last hours of the three-day garlic festival, a beloved annual tradition that draws thousands of attendees of all ages. He injured 15 people and killed three – a six-year-old boy, a 13-year-old girl and a man in his 20s – before being shot dead by police officers, who rushed him within a minute of bullets being heard.

The Giffords Law Center to Prevent Gun Violence ranks California first in the nation for having the strongest gun laws.

California raised the minimum age to purchase a rifle to 21 in 2018. And last week, a federal judge upheld California’s ban on owning, manufacturing or selling semiautomatic rifles and so-called “bullet buttons”, rifle attachments that allow shooters to reload more quickly. The state has banned semi-automatic weapons for 20 years. The bullet button ban dates from 2016.

Nevada, on the other hand, is ranked 25th in the Giffords Center’s ranking.

Big Mikes Gun and Ammo, the Nevada store where the gunman bought his weapon, said in a statement on its Facebook page that the shooter had bought the rifle off of the store’s internet page.

“The reach of the California law ends at our border,” California’s attorney general, Xavier Becerra, told the San Francisco Chronicle, “and so we cannot control what other states do, and that’s what makes it so tough. We may have progressive gun laws, but if other states don’t match us, we have to rely on the ability to catch” the person.

Related: Gilroy grieves after gunman kills three young people at California garlic festival

Several lawmakers have pointed at Sunday’s shooting to once again call for a federal law that would close this cross-state loophole.

“The gun used by the Gilroy shooter was an AK-47 type assault rifle. This weapon is illegal to buy or possess in California, which appears to be why the shooter crossed into Nevada to buy the gun,” said Senator Dianne Feinstein in a statement. “The assault weapons ban legislation I introduced earlier this year would have prevented that sale from happening. It’s time for Congress to debate this bill and vote on it.”

Feinstein continued: “There are other bills out there that deserve to see the light of day including bills to require comprehensive background checks, help establish extreme-risk laws, prohibit the purchase of high-capacity magazines and eliminate loopholes that allow prohibited individuals [to acquire] guns.”

“This loss cannot be in vain,” tweeted the California congresswoman Jackie Speier early Monday.

Speier is looking to close the gap, as one of 190 members of the House who co-sponsored a bill that would ban the import, sale, manufacturing or possession of semiautomatic assault weapons and large capacity ammunition feeding devices on the federal level.

The California representative Eric Swalwell, who campaigned briefly for the Democratic 2020 presidential nomination and was the only one of two dozen candidates to focus his platform primarily on stronger gun control, was another one of the bill’s co-sponsors.

Senator Kamala Harris, who represents California, has called for a renewal of a federal assault weapons ban as well. She has stated that should she be elected, she will give Congress 100 days to take legislative action on gun violence, and if lawmakers cannot reach a consensus, she will take executive action.

The gun laws differ so vastly from state to state that a small California city located near the Nevada and Arizona borders voted this month to ask state legislators to allow gun owners from other states to carry registered firearms in the town.