Again? Jim Gard wondered as the fire alarm blared through the classrooms and hallways of Marjory Stoneman Douglas High School.

It was around 2:20 p.m., the school day crawling toward final dismissal. Gard was leading his advanced math class through logarithms — exponential growth and decay — in preparation for a test on Friday. The South Florida campus had already had one fire drill that morning. Two drills on the same day? Weird, he thought, figuring it was an accident. “We have a cooking department,” the veteran teacher told The Washington Post on Wednesday. “They burn things sometimes.”

But then the school’s public address system squawked: Evacuate. Gard’s students were heading out of his second-floor classroom when they heard a string of pops — sharp and staccato.

“Everyone back in the classroom,” he yelled from the doorway. Only six of his students hustled back inside. The system then barked again: code red. That meant active shooter, Gard knew from his training. He snapped the classroom’s locks, cut the lights and huddled his students into a closet at the back of the room.

Even then Gard wondered whether this was some elaborate test. He didn’t own a firearm, didn’t know how real gunshots sounded. The school had also talked about inviting law enforcement representatives to the campus for an active shooter exercise, an unannounced staging to see whether, after all the training and assemblies and talks about awareness, Stoneman Douglas was ready for the worst-case scenario.

Gard and his students waited. When the teacher heard helicopters thump overhead and the growing scream of police sirens, he knew what was happening outside his classroom was no drill.

On Wednesday an armed shooter attacked the campus, a massive grade 9-through-12 high school serving about 3,000 students in Parkland. The Broward County Sheriff’s Office had identified the attacker as Nikolas Cruz, a 19-year-old who had previously attended the school but was kicked out for “disciplinary reasons.”

According to law enforcement, Cruz, armed with an AR-15 rifle, marched through the hallways shooting students and staff, firing his weapon into classroom windows. Seventeen people were killed in the attack.

Nikolas Cruz, 19, is the man suspected of fatally shooting at least 17 people at a South Florida high school on Feb. 14. Here's what you should know. (The Washington Post)

Mixed with the shock of Wednesday’s attack is a familiar frustration. As The Washington Post reported Wednesday, since the 1999 Columbine shooting in Colorado, more than 150,000 students attending at least 170 schools have experienced campus shootings. The Parkland shooting is now among the top 10 deadliest mass shootings in U.S. history. Three of the incidents on the list have happened in the last five months. Like many high schools, Marjory Stoneman Douglas High School trained for an attack.

“We did everything that we were supposed to do,” Melissa Falkowski, a teacher at the school, told CNN’s Anderson Cooper. “Broward County has prepared us for this situation, and still to have so many casualties, at least for me, it’s very emotional.”

Students echoed the same sad resignation.

“I’m kind of surprised it happened here, but I’m not really shocked,” 17-year-old Ryan Kadel told The Post. “School shootings happen all the time, and then the news just forgets about them.”

Parkland sits on the northwestern edge of Broward County, a 20-minute drive from downtown Fort Lauderdale. Sandwiched between Miami-Dade and Palm Beach counties, Broward has a distinctly suburban feel, neither as flashy as its southern neighbor nor as soaked in old money as the county to the north. From Fort Lauderdale beach, Broward stretches on, mile after mile of palm-studded housing developments and strip malls, until it abruptly ends at the saw grass fields of the Everglades, not far from Marjory Stoneman Douglas High School.

Built in 1990, the school  pulls its student body from Parkland and Coral Springs, the Sun-Sentinel reported. Security guards on golf carts patrol the grounds. There are built-in whirlpools in the locker rooms. A gazebo decorates the campus. Students dubbed it the “emo gazebo,” because it was where outcasts gathered, the Daily Beast has reported.

On Wednesday, as the fire alarms cut through the hallway, students were also confused about whether this was a drill or a real threat.

Andy Pedroza, an 18-year-old senior, was heading back to his classroom on the third floor when he heard the gunshots.

He bolted for a nearby bathroom, ducking into a stall. He contemplated climbing up on the seat to hide his feet but the toilet was too slippery.

“In the moment I was shaking,” he told the Sun-Sentinel. “I was shaking like a Chihuahua who was terrified in a thunderstorm.”

Nathanael Clark describes hearing screams for help outside his classroom as shots rang out at his Parkland, Fla., high school on Feb. 14. (Dan DeVivo, Amber Ferguson, Elyse Samuels/The Washington Post)

Nathanael Clark was in a classroom on the first floor when the gunshots sounded.

The teacher locked the door. Clark did not realize the shots were real until debris started falling from the room’s walls as bullets slammed in from outside.

“I heard a girl screaming for help,” Clark told reporters. “And we can’t open the door because if we open the door the shooter would come inside and kill all of us. I heard gunshots after the screams.”

Mackenzie Hill had just left her AP Psychology class for the bathroom.

Her twin sister, Meghan, a student in the same class, stayed behind. The bathroom was closed, so Mackenzie made her way upstairs. Then she heard the bullets. Ten, maybe 15 gunshots.

Looking to her left, all the way down the mostly empty second-floor hallway, Mackenzie noticed a man holding a large gun.

“I immediately knew it was him,” she told The Post, recognizing Cruz’s face. She remembered the boy from her middle school, and from the dollar store in town. She recalled his terrifying Instagram posts about wanting to kill people. “I always had a bad feeling about him,” she said.

She rushed to the classroom closest to her, knocking on the door, but it was locked. Teachers and students had already begun cowering in their rooms and were instructed not to let anyone in. Feeling panicked and terrified, knowing the shooter was right down the hallway, Mackenzie knocked on another door.

The teacher must have “seen the fear on my face,” she said. She didn’t know the teacher, she said, but “without him, I don’t think I’d be alive today.” He let her in. Mackenzie darted to the back of the classroom to hide with the other students, few of whom she knew.

Crying hysterically, Mackenzie noticed that a girl next to her was having trouble breathing. The girl had asthma and didn’t have her inhaler on her. Mackenzie tried to calm her down, worried she might have an attack.

“Take deep breaths. Don’t talk. It’s going to be okay,” Mackenzie recalled saying to the girl.

Mackenzie hid beside a desk, burying herself under some of the other students. At one point, the students heard a loud banging on the door. But the shooter never entered the classroom. Mackenzie texted a photo to her parents, showing her hiding under a desk, tears falling down her face.

“I love you guys so much,” she texted, saying this could be the last time she speaks with them. Above all else, Mackenzie thought about her twin sister, a floor below her, in the AP Psychology classroom. The shooter was on her floor, Meghan texted her.

“I love you,” Meghan wrote in text messages that Mackenzie would later delete, to erase all memories of the nightmare. “Please be safe.”

But suddenly Meghan stopped sending text messages. She was worried Mackenzie’s ringtone might be on loud and could tip off the shooter.

For about 40 excruciating minutes, Mackenzie wondered if her sister was okay.

In Meghan’s classroom, the locked door didn’t stop the shooter and his gun. Smashing through the window in the door, and standing in the hallway, the gunman fired into the classroom.

One of the bullets skimmed right past Meghan’s ear, leaving an intense ringing sound in its path. Behind her, the bullet struck Meghan’s friend in the knee.

Four people in the classroom were shot, Mackenzie said.

“No one was crying,” Mackenzie said of the injured students, recounting her sister’s memories. The wounded were just moaning.

Hiding behind a desk, Meghan saw a girl lying on the floor, bleeding. Even though the teacher had instructed them not to move, Meghan took off her jean jacket, throwing it over the girl’s body, Mackenzie said.

In Mackenzie’s classroom upstairs, a police officer broke through the glass in the door, preparing the students to evacuate. The officer noticed that one of the students was wearing a bulletproof vest. Asked about the vest, the student explained he had carried it with him to school because his father is a police officer, Mackenzie recalled.

Moments later, the officer escorted the class out of the school, instructing them to hold onto each other’s shoulders in a line and to keep their heads down.

But Mackenzie couldn’t help but catch glances of the carnage around her. She peered inside a classroom and saw blood all over, with at least one body on the floor. Once outside the building, she saw the school security guard lying on the ground.

As soon as she was out of the building, she called her sister. Meghan, her sister learned, had already evacuated the school and reunited with their parents.

Across the area, frantic parents were learning of the attack and heading for the school, trying to piece together information on their children. As police cleared the hallways, cellphones — both left behind by fleeing students and on the bodies of victims — buzzed with unanswered messages and calls.

John Crescitelli, a doctor with a 15-year-old daughter at the school, learned about the shooting at work. A familiar feeling — empty, hollow — hit him. His brother was a firefighter in New York City during the 9/11 attacks. All those years ago, Crescitelli didn’t know whether his brother was dead. Now he didn’t know about his daughter. The two were eventually reunited.

“I never thought I would live across the street from a Columbine,” he told reporters.

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