Bend, Oregon - Kristen Vanetsky and her family moved to Bend, Oregon, after a shooting in their New Mexico neighborhood, choosing Silver Rail Elementary for her grandson because they considered it safer.

But their world was shattered this week when a 16-year-old entered the school and opened fire, shooting dead three children and a teacher, and leaving another child and educator critically wounded.

An armed bystander who pursued the gunman into the school shot and killed him.

The tragic events, Vanetsky told AFP Friday morning outside the school, are "unthinkable."

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The 52-year-old, whose 10-year-old grandson attends the school, said the mass shooting "just took away all the innocence" of the school's children, disrupting their sense of safety.

She said she went to the school "trying to make sense of what's going on."

"Who would do this to little kids?"

Thursday's massacre in Bend – a city of about 100,000 people in central Oregon – is the latest of 371 mass shootings that have occurred in the US just this year, according to the tracker Gun Violence Archive.

It "just doesn't stop," Vanetsky said.

She said she is grateful for the actions of the man who fired back against the shooter, but notes the scenario's inherent contradictions, which underscore the ongoing debate over gun control in the US.

"It's very weird, to have a gun solve the problem of a gun," she said. "I can't wrap my mind around it."

"The whole thing could've been a lot worse had somebody not stepped in and shot the shooter," she continued. But now, "the shooter has to live the rest of his life knowing that he shot a 16-year-old to keep other babies from being shot."

"It doesn't make sense," she said tearfully.

Bend, a popular destination for its natural beauty and outdoor recreation scene, "is devastated," Vanetsky said.

"We're a close town of people, and we look out for each other."

And yet, the perpetrator of Thursday's attack was a resident of the city itself.

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Authorities have not yet offered details regarding motive or any connection to the school. They did specify that a long gun was used, and media reports indicate the shooter's mother had purchased the weapon.

"I don't understand why a mom would buy a teenage boy a weapon like that," said Vanetsky.

Less than 24 hours after the shooting, Silver Rail Elementary School, which serves more than 400 students, was cordoned off with yellow crime-scene tape.

A few cars and bicycles remained stranded in the parking lot.

At the school's main entrance, neighbors and parents had created a memorial with flowers, candles, and toys to honor the children – aged five, eight, and 11 – and the educator whose lives were cut short Thursday.

Vanetsky said her grandson was struggling at home in the wake of the trauma he'd been through.

"My grandson should be in his classroom, with all of his friends," she said, her gaze turning towards the school's second floor. "Everybody should be in there learning, having fun, looking forward to their weekend, and it's just vacant."

"There's nothing. Even the birds are not here."