The warning had come that morning by phone to Apalachee High School: There would be shootings Wednesday at five schools.

And the unknown caller – law enforcement officials would later confirm – warned Apalachee would be the first. Still, students all across Winder, Georgia, streamed into their classes Wednesday, heading to first period, then second.

For Lyela Sayarath at Apalachee High, it was Algebra 1.

When the quiet boy sitting next to her got up during the lesson and left, the door closing and automatically locking behind him, Lyela thought nothing of it, she said.

This boy was known to skip class.

But then he came back.

The 14-year-old knocked on the classroom door, and a girl got up to let him back in before jumping back, startled.

The boy had an assault rifle.

Through the small window of the locked classroom door, Lyela saw the boy with the gun turn right toward another classroom, she later recalled.

Then, gunshots exploded at Apalachee High School.

A 10-minute walk away, Haymon-Morris Middle School eighth-grader Tim Mosher was also in second period, Connections B: band, when he heard a gun go off.

The 13-year-old percussionist grabbed a big drum and got ready to throw it at the shooter.

But then an announcement was made: Their school was on lockdown.

Tim sat down, back against the wall. Someone turned off the lights. No one said a word.

Like so many American schoolchildren, they had trained for this and knew to stay quiet. They did not yet know their city of Winder, Georgia, was about to become the site of the deadliest US school shooting so far this year.

Right about then, Tim’s mom, Pam Mosher, was standing in a Publix supermarket down the road. Her phone buzzed with a message from her son’s school:

“Parents, At this time we are taking caution, and the school is in a hard lockdown due to our neighboring school – Apalachee- being in a lockdown. HMMS students are safe. Please do no attempt to come to the school at this time.”

Then, police cars zoomed by – sirens and lights blaring – in the direction of the schools’ shared campus.

Mosher knew something was wrong.

In Lyela’s algebra class, students dropped to the floor and crawled to the corner, piling together as the teacher turned off the lights.

Lyela, 16, pushed desks in front of herself and her classmates. She told others to get low.

Also in class at Apalachee High, Ethan Haney heard some nine gunshots outside his classroom and closed the door, he’d later tell his mom. The 17-year-old and others pulled chairs and tables to block it.

Like so many kids taking cover just then, Ethan’s mind went to his loved ones. His fingers went to his device.

‘No matter what you do, keep texting me’

Gunshots echoing through the high school hallways sounded to 16-year-old student Julie Sandoval like heavy books getting slammed down.

For Janice Martinez, it was like someone playing around outside.

Within seconds, though, that illusion was shattered: Her teacher was shaking. Her classmates were crying.

“The noise kept getting louder and louder,” Janice recalled. “I told everybody to get down. Get down.”

Julie didn’t know what to do other than hide and text her parents, worried about her younger sister, also a student at the high school. Sobbing, Julie told her parents how much she loved them – and apologized because she felt she hadn’t been “a perfect daughter.”

Macey Right, 14, also texted her mother: “Mom, I’m scared. I hear gunshots. Please come get me.”

Macey heard screams, too, and “people begging not to get shot, and then people sitting beside me just shaking and crying,” she later recalled.

Her mom, Anetra Pattman, a teacher at an alternative school about five miles from Apalachee High, tried to comfort her daughter.

“No matter what you do, keep texting me, just text me, just text me, to let me know that you’re OK,” Pattman recalled texting to her child as her own school soon went into lockdown: Pattman switched off her classroom lights and kept her class silent.

Shana McMillan got horrifying messages from her daughter as the girl hid in the room across from a classroom where a teacher had been killed. Her daughter’s teacher had told her students to get in the corner, then stood over them to “protect them just in case the shooter came in the room.”

Soon, students from across the hall rushed to her daughter’s room, crying. “She was scared,” McMillan said. “She thought they were maybe coming to her classroom next.”

Macey and other girls held hands together to pray. Moments later, they were disrupted by banging and yelling.

A classmate told Macey one of her friends had been shot in the shoulder.

Authorities got the first calls of an active shooter on campus at 10:20 a.m., after someone pressed a wearable panic button issued just a week earlier to teachers, the Georgia Bureau of Investigation director and the Barrow County sheriff later would say.

Within minutes, school resource officers confronted the shooter.

The suspect, a 14-year-old boy, got on the ground and was taken into custody, authorities said.

Outside the school, the wait for answers was agony.

Pam Mosher left the grocery store. She went home. She kept getting the school’s texts.

11:38 a.m.: “Haymon-Morris Midd: Parents and Guardians, HMMS is still on a hard lockdown. HMMS students are safe and secure. Please be patient.”

Now, word was starting to spread – on text chains, on Atlanta news stations, on CNN – of four people shot dead at Apalachee High.

Mosher tried to be patient, tried to trust her neighbors, trust the system. “We’re in Barrow County,” she would say afterward. “I know what’s in those cop cars. I know they train for this.”

Kathrine Maldonado woke up late Wednesday to texts from a friend. While the teenager had overslept, their school had gone into lockdown.

Kathrine’s friend said she was OK, then started texting group chats.

A friend, they learned together, had been killed.

“I started crying,” Kathrine said, “and I just got mad.”

‘Keep your head up, keep your head up’

With the suspect detained, officers streamed into Apalachee High, evacuating students from classrooms as paramedics tended to the wounded. Helicopters swirled overhead.

By then, the fallout was coming into focus: Two teachers and two 14-year-old students were dead, and nine others – eight students and one teacher – were injured and taken to hospitals, according to the Georgia Bureau of Investigation.

Julie Sandoval cried as she heard police coming into the classroom.

“Let me see your hands,” they yelled.

“I started bawling my eyes out because my initial reaction was obviously scared because I had a gun pointed at me. But then I was, like, ‘OK,’ that obviously means that I’m OK because the police are here, and I’ll be fine,” Julie said.

Students walked the school’s hallways with their arms up as officers instructed them to: “Keep your head up, keep your head up.”

 Mark Gorman holds a candle during a vigil on September 4 for the slain students and teachers at Apalachee High School. Mandatory Credit:Mike Stewart/AP via CNN Newsource

‘I finally got to her, and she was devastated’

For all those hours, Tim Mosher had sat against the wall in band class. He didn’t watch the clock, he said. At some point, snacks and drinks got delivered to the musicians waiting in Connections B.

Tim got a Lucky Charms snack bar and a small carton of milk, cafeteria-style.

By mid-afternoon. Pam Mosher got another text:

“Haymon-Morris Midd: Law enforcement has now given the ok to lift the lockdown … Thank you.”

So, Mosher headed toward Haymon-Morris Middle School.

By then, hundreds – maybe thousands – of others were streaming toward the campus, and Pam couldn’t quickly get close. The parents and grandparents and neighbors and friends of the children of Winder had choked the few roads to their city’s schools for more than mile in all directions, brake lights bright red over the horizon.

So, Mosher fell in with pockets of others who left their vehicles in long rows on sidewalks and roadway shoulders and walked – pushing strollers, maneuvering a leg-cast scooter, hoisting toddlers on hips and shoulders – under a late-summer sun toward the nexus of flashing blue lights.

Along the way, neighbors had set up a card table and handed out water, sports drinks, granola bars, applesauce packs, cheese and peanut butter crackers, gummies and cold cubed watermelon.

“It’s afternoon, and they haven’t eaten since breakfast,” organizer Chris Comfort said of many of the students who passed by.

“There were some kids who hadn’t eaten since last night because they didn’t have time for breakfast this morning. They were on their way to school,” said her daughter, Geaux, who’s homeschooled.

“It’s hot, and it’s scary,” the 15-year-old added. “I hated that my friends and even kids that I don’t know are having to go through this.”

As families scrambled to reunite outside the school, Lyela recounted the shooting to a CNN reporter. She described the moment she saw a friend who had been in a classroom where shots were fired.

“He saw it. He saw somebody get shot. He had blood on him. He was kinda limping,” Lyela said. “He looked horrified.”

Meanwhile, Macey and her mom reunited in a tearful embrace.

“I finally got to her, and she was devastated. We hugged and cried for a while,” Pattman said. “You never, never, ever, ever, think it would happen to you or to one of your children.”

Erin Clark, who had texted love to her “baby,” found Ethan safe by the bleachers.

And when Pam Mosher finally got to Tim’s school, police, sheriff’s deputies and SWAT officers had blocked every entrance, she said.

Mosher showed her ID. Tim confirmed he was hers.

And mom and son started a long walk toward home.

CNN’s Michelle Krupa and Isabel Rosales reported from Winder, Georgia. CNN’s Zenebou Sylla, Taylor Romine, Sharif Paget, Alli Gordon, Nick Valencia and Dakin Andone contributed to this report.