FARMINGTON, New Mexico — A quiet New Mexico neighborhood became a scene of inexplicable horror when a high school student with an AR-style rifle fired a torrent of bullets from the yard of his home.

Beau Adam Wilson, 18, dropped the assault-style weapon and continued his deadly rampage with two handguns, walking through the Farmington community and shooting houses and cars at random, police said.

By the end of Monday’s rampage, three elderly women were killed. Six others were wounded. The gunman was killed by police. And another seemingly safe place in America – a residential neighborhood – is now grappling with the shock and trauma of a mass shooting.

In just the first five months of this year, the US has suffered at least 227 mass shootings, with at least four victims shot.

While the motive remains a mystery, new details could emerge Thursday afternoon when Farmington police release body camera footage from the incident.

How the carnage unfolded

The gunman, wearing a bulletproof vest, fired at least 141 rounds from his yard with the rifle Monday morning before ditching it in some bushes and leaving the property with two handguns, officials said.

The shooter walked through the neighborhood and “randomly fired at whatever entered his head to shoot at,” before police fatally shot him, police Chief Steve Hebbe said in a video statement.

“There were no schools, no churches, no individuals targeted,” he said.

More than 200 911 calls flooded in to authorities as gunfire pierced the neighborhood, nestled in a commercial hub near the Southwest’s Four Corners.

Armed with .22-caliber and 9 mm guns, the assailant kept shooting as he walked toward a church, where he was killed by police, Hebbe said.

The mass shooting killed three women on morning drives.

Gwendolyn Schofield, 98, and daughter Melody Ivie, 73, were killed in their car.

Shirley Voita, 79, who also was shot in a car and later died at a hospital, authorities said.

The six people wounded include Farmington Police Sgt. Rachel Discenza, who was shot during a gunfight with the killer. New Mexico State Police officer Andreas Stamatiadas was shot while driving to the scene.

Both officers have been released from the hospital, along with the four other wounded victims, Farmington Deputy Chief Baric Crum said.

More than 150 shell casings littered the neighborhood over a “wide and complex scene” that spans more than a quarter of a mile, authorities said.

In total, the assailant fired at three vehicles and six houses, though none of the victims was in a residence.

“The amount of violence and brutality that these innocent people faced is something that is unconscionable to me,” Deputy Chief Kyle Dowdy said.

“I don’t care what age you are. I don’t care what else is going on in your life. To kill three innocent elderly women that were just absolutely in no position to defend themselves is always going to be a tragedy.”

10 more guns and 1,400 rounds of ammo

Authorities have said they believe two of the guns used in the rampage were legally owned by a family member and they are investigating how the shooter got them.

Wilson, who turned 18 in October, purchased the third gun in November. He bought three magazines for the rifle just two days before the rampage, the chief said.

“We’re certainly looking at the circumstances by which he procured the (rifle) and some of the other weapons, and part of the investigation will take us into what were the circumstances by which the other weapons had been obtained,” the Farmington police chief said.

Aside from the three weapons used in the attack, 10 more guns and 1,400 rounds of ammunition were found in the shooter’s house, the chief said.

After the gunman was killed, authorities found a short, handwritten note in his pocket and were trying to “piece together” the note’s meaning, Hebbe said.

Wilson had only “minor infractions” with law enforcement before the violent attack, Dowdy said.

Some relatives interviewed by law enforcement expressed concerns about Wilson’s mental health, the deputy chief said, but it’s not clear whether he had been diagnosed with any issues.

“We’ll end up finding in the next couple of days what medication if any he was under, if he was under a doctor’s care in some form or fashion,” Hebbe said.

The attack left Farmington “shaken to the core by an unthinkable incldent that robbed families of their loved ones,” Mayor Nate Duckett said.

It came just one day before graduation at Farmington High School, where the gunman was a student.