WILLIAM BRANGHAM: One year ago, today, a gunman entered Robb Elementary School in Uvalde, Texas, killing 21 people, including 19 children.

It was one of the worst school shootings in U.S. history.

AMNA NAWAZ: Here in Uvalde, those 21 families are still mourning their loss.

The survivors are living with trauma.

And a community is still searching for answers.

Among those we spoke to here is Javier Cazares.

His 9-year-old daughter, Jackie Cazares, was among those killed today.

And Javier says, one year later, he's struggling to move on.

AMNA NAWAZ: How often do you think about that day?

JAVIER CAZARES, Father of Shooting Victim: Every day.

AMNA NAWAZ: Every day.

JAVIER CAZARES: It's nonstop.

It's a nightmare we can't -- I can't wake up from.

AMNA NAWAZ: One year ago, Javier Cazares frantically waited with other parents outside Robb Elementary as gunshots rang out.

Trapped inside, his 9-year-old daughter, Jackie, who loved dancing, and dogs, and dreamed of one day going to Paris.

JAVIER CAZARES: She was the light of our life, sassy, funny, a little jerk sometimes.

She just had that spark in her life where she touched people.

AMNA NAWAZ: Jackie was one of 19 fourth-graders and two teachers killed by an 18-year-old gunman with an AR-15-style rifle in one of the worst mass shootings in Texas history.

You dropped her off that day.

JAVIER CAZARES: Yes, ma'am.

AMNA NAWAZ: Do you remember the last thing you said to her?

JAVIER CAZARES: I blew her a kiss goodbye.

And she did the same.

And that was the last time I saw her.

AMNA NAWAZ: Dr. Roy Guerrero was at the hospital that day as children were brought in.

DR. ROY GUERRERO, Uvalde Pediatrician: I still don't believe it.

I still can't believe what I saw.

These are 9- and 10-year-old little kids ripped apart, that they had to in some instances smear blood on themselves to survive.

AMNA NAWAZ: Dr. G, as he's known, is Uvalde's only pediatrician.

Five of the victims were his patients.

Many of the survivors still are.

DR. ROY GUERRERO: By no means are any of these children back to normal.

I have kids that are terrified to even step back in the classroom again.

I have kids that are in full-blown PTSD, having nightmares and being paranoid and seeing the killer and feeling that he's coming after them.

And, so, yes, I don't think there is true healing from this, even in the long term.

AMNA NAWAZ: In the year since the shooting, residents and media have fought for more information like security camera and body camera footage to be released.

Questions remain about why it took nearly 400 officers on the scene an astonishing 77 minutes before they confronted the gunman, even as emergency calls poured in, some from students stuck inside.

MAN: He's inside the school shooting at the kids!

EMERGENCY DISPATCHER: Uvalde County 911.

STUDENT: There's a school shooting, Robb Elementary School.

STUDENT: Send help.

Some of my teachers are still alive, but they're shot.

AMNA NAWAZ: Days after the shooting, the head of the state's Public Safety Department admitted waiting was a mistake.

STEVEN MCCRAW, Director, Texas Department of Public Safety: From the benefit of hindsight, where I'm sitting now, of course, it was not the right decision.

It was the wrong decision, period.

AMNA NAWAZ: An investigation by Texas lawmakers later found systemic failures.

But families of those killed want answers and accountability.

They have packed school board meetings, demanding officers be fired and security improved.

They filed a class-action lawsuit against the city, school district, and multiple law enforcement agencies.

PROTESTERS: Raise the age!

AMNA NAWAZ: And they have pushed for gun violence reform, like raising the age to purchase a semiautomatic weapon in Texas from 18 to 21.

That effort failed in the state legislature.

BRETT CROSS, Uncle and Guardian of Shooting Victim: Why do these people who sit in power sit there and do absolutely nothing while our children are slaughtered?

AMNA NAWAZ: Brett Cross' 10-year-old son, Uziyah Garcia, was killed that day.

BRETT CROSS: I'm not a political person.

All I want is justice and accountability for my son, his classmates and teachers.

That's all I want.

And I don't want any other child to go through what my son did.

I don't want any other parent to have to have a funeral for their child.

AMNA NAWAZ: Robb Elementary is shuttered.

Officials plan to demolish it.

Last fall, Uvalde students returned to other classrooms, but not all of them.

Do you ever miss being in school, in a classroom?

ZAYON MARTINEZ, Student: Kind of.

AMNA NAWAZ: Nine-year-old Zayon was at Robb in second grade during the shooting.

Since that day, he's refused to return to a classroom, and only attends virtually.

ADAM MARTINEZ, Father of Zayon Martinez: Imagine if you were a child, an 8, 9, or 10-year-old child, and you know that your friends got slaughtered, to where you couldn't even identify them.

AMNA NAWAZ: His father, Adam, raised in Uvalde, has become an activist and a leading voice for parents whose children survived that day.

ADAM MARTINEZ: You will see a lot of survivor's guilt.

People hold it in because they're like, well, my son survived, my daughter survived.

So a lot of times, they're afraid to speak out.

But it hurts when you hold it in.

And, sometimes, you just got to say what you feel, because he was there and he's not the same child anymore.

JAVIER CAZARES: It catches her eyes beautifully.

AMNA NAWAZ: Every week, Javier visits Jackie's mural downtown.

He's on a mission to remember and fight for change.

JAVIER CAZARES: And it hasn't happened.

And it is saddening, because, I mean, what more does it take?

I mean, it's our babies.

AMNA NAWAZ: He checks on her cross at the town square memorial.

That's the same photo that you have on your shirt, right?

JAVIER CAZARES: Yes, ma'am.

AMNA NAWAZ: What's that from?

JAVIER CAZARES: from her first communion.

She had her first communion on Mother's Day of last year.

And that's actually what we buried her in as well.

AMNA NAWAZ: And back home, he's kept her room exactly as she left it that day.

You haven't touched it in the last year?

JAVIER CAZARES: No.

AMNA NAWAZ: Why not?

JAVIER CAZARES: Well, I mean, that's how she had it.

And then she was particular, but, I mean, she had her things nice and neat.

She had her shirt and shorts folded up nice and neat.

And so I didn't want to bother that.

That is something that, if I change it, I'm going to miss.

AMNA NAWAZ: Do you go in the room?

You do?

JAVIER CAZARES: I go in there maybe twice, three times a day.

Of course, and then, before we go to bed, I pray like when she was there.

Sometimes, on a certain day, I just go and talk.

I just walk around and just look at everything in there.

I'm sure fathers say this about their daughters all the time, but she was special.

AMNA NAWAZ: The pain is still so fresh here for these families.

But last year opened up new divides here in this community over how to move forward, not just on accountability, but also on gun violence prevention