AMNA NAWAZ: Welcome to the "News Hour."

Georgia is mourning the lives of four people killed in a high school shooting yesterday.

Nine others were injured.

GEOFF BENNETT: Today, reports of the 14-year-old suspect's past run-ins with law enforcement raised even more questions about his motive, how he got access to a gun and how potential warning signs went unaddressed.

At Apalachee High School, some students returned today to grieve at a makeshift memorial, a quiet morning after yesterday's tragedy.

MAN: Bless us and walk with us each day as we go forward.

GEOFF BENNETT: The community gathered for a vigil last night after a 14-year-old student opened fire outside his algebra classroom.

Four people, two students and two teachers, were killed.

Those who survived still processing what they'd witnessed hours earlier.

LANDON CULVER, Student: You could hear gunshots just ringing out through the school.

And, like, you're just wondering which one of those is going to be somebody that you're like best friends with or somebody that you love.

GURAY CHAPMAN, Student: I still don't believe this is real.

Like, I knew a girl that got shot in her leg, and it really broke me, because she was like a sister to me.

And I don't know how to react to it.

GEOFF BENNETT: Students recounted ducking for cover in their classrooms as gunshots rang through the hallway.

Within minutes, officials say, the shooter surrendered to school resource officers.

Questions remain about how the teenage gunman obtained an assault-style rifle, as more information emerges about his past encounters with law enforcement.

In May 2023, the FBI traced online posts from an individual threatening to shoot up a middle school, according to multiple news reports.

That led authorities to the youth, who was then 13.

He denied making those comments.

His father insisted his son did not have access to hunting guns kept inside their house.

Authorities alerted nearby schools to monitor him, but he was not arrested or further detained.

In a home search yesterday, according to The New York Times, police found evidence that the gunman was -- quote -- "obsessed" with the 2018 school shooting in Parkland, Florida.

He's set to appear in court virtually tomorrow.

Among his victims, two 14-year-old students, Mason Schermerhorn, whose family described him as a lighthearted teen and a lover of Disney World, Christian Angulo, whose friends called him a free spirit with a chill attitude, and two faculty members, 53-year-old Christina Irimie, a devoted math teacher described as patient and caring, and 39-year-old Richard Aspinwall.

He also taught math and coached football as the team's defensive coordinator.

ISAIAH HOOKS, Student: Coach was an amazing guy.

He pushed us to be great at what we did for our team.

So it was really hard to lose someone that pushed himself to really make us better and to make sure that we're better at what we do.

GEOFF BENNETT: Apalachee joins a long list of American schools that now bear the scars of gun violence.

And it's the 30th mass killing of 2024, in which four or more people are murdered in a 24-hour period, as defined by the FBI.

Such incidents have claimed at least 127 American lives this year alone.