A healthcare worker returning fire on a 24-year-old gunman who killed three people and wounded several others an In-N-Out Burger in Twin Falls, Idaho, has said his impulse to confront the attacker was “automatic” and “mechanical”.

That description from 35-year-old Jordan Salinas came in an interview with the Idaho Statesman that was published on Sunday, providing a detailed account of actions that police credited with limiting the number of victims in the attack a day earlier.

Salinas said he was headed out for a horseback riding date with his girlfriend when they stopped at the burger restaurant for lunch at about 2.30pm on Saturday. Salinas saw people fleeing and heard the “pop-pop-pop” of gunfire, according to what he told the Statesman.

He said he ran toward the sound in an “automatic” and “mechanical” response, drawing from a shoulder holster a semi-automatic pistol with a suppressor fixed to its barrel.

Salinas said he had been training with firearms seriously since a deadly shooting at a mall in Boise, Idaho – about a two-hour drive from Twin Falls – left two dead and four wounded.

One of those killed was identified on Monday from social media posts by loved ones as 23-year-old Ashley Garibay, of Stockton, California. Garibay was an employee at the newly-opened outlet of the restaurant chain.

Salinas said he watched on Saturday as an attacker later identified as Chad Williams, standing by the drive-through window, lifted a rifle to his shoulder and fired toward cars.

Salinas countered by raising his pistol with both hands and firing. “He did not like it when bullets started firing both ways,” Salinas told the outlet.

Police later said the attacker died from a self-inflicted gunshot wound, crediting Salinas and an off-duty officer for diverting the shooter with return fire.

“We believe their actions helped drive the suspect away from the scene, preventing further casualties,” said Matthew Hicks, the Twin Falls police chief, at a news conference. “We want to take a moment and commend the actions of the off-duty officer and the citizen – and their heroic action to stop this incident.”

Jack Johnson, the Twin Falls county sheriff, said: “These people are true heroes in our community. They diverted the shooter and without a doubt saved many lives.”

Williams, 24, killed three victims before dying by his own hand, police said. Police added that he wounded seven others at the recently opened restaurant in the southern Idaho city of about 56,000 people.

Two of the wounded were treated at a hospital and discharged; three were listed as stable; and two were in critical condition.

Salinas – a full-time caregiver of his brother, who gets around in a wheelchair – said he felt “no fear” during the confrontation with Williams after following four steps he had learned in firearm training.

Those steps, he said, were “observe, orient, decide [and] act”.

“There’s a task that needs to be done, and we’re the ones who need to do it,” he told the outlet.

The decision to take up firearms training, he said, came after he reasoned that gunmen go after “soft targets”. And a person in a wheelchair, and the aide at his side, would be exactly that, he said.

“Everyone says, ‘It’s not going to happen here,’” Salinas said. “But what if it does?”

Salinas’s interview and the police’s praise of him came amid a debate over the correct response of bystanders to mass shootings. Some witnesses to Saturday’s attack in Twin Falls were reported to have slowed their cars and shouted at Williams.

As of Monday morning, there had been at least 280 mass shootings reported across the US so far this year, according to the Gun Violence Archive.

The archive, a non-partisan resource, defines mass shootings as cases in which four or more victims are shot or wounded.

The high numbers of mass shootings annually reported in the US have driven calls for more substantial federal firearms restrictions. But Congress has not implemented such gun control over the years.