PARKLAND, Florida—A gunman killed 17 people at a south Florida high school with a high-powered rifle, as students recorded the massacre on their phones.

The attack on Marjory Stoneman Douglas High School—in an affluent area about 40 miles north of Miami and one of largest schools in the state with about 3,000 students—is the deadliest school shooting since the Sandy Hook massacre in 2012. The gunman, identified by Broward County Sheriff Scott Israel as Nikolas de Jesus Cruz, opened fire with an AR-15 rifle inside and outside the school. Cruz, 19, was taken into police custody after he fled the school on foot.

Milan Parodie, 15, told The Daily Beast that students were outside when the gunfire started because the fire alarm had gone off.

“Probably about 5-7 minutes after we went outside, I heard five gunshots,” she said. “We saw someone run from the other side of the school, where the shooter was. Everyone got scared and started running away. Teachers were running, and that’s when I got scared. I’ve never seen a teacher run.”

Milan said her brother, Roman, was sheltered in a classroom during the attack.

“Someone knocked on the door and asked to be let in, and they locked the door and stayed quiet,” she said.

Roman sent Milan a video of a person shot dead inside a classroom.

Throughout the school, students recorded the shooting on their phones and uploaded the harrowing footage to social media for the world to see. In one video, the defeating blasts of rifle fire nearly drown out shouts of “Holy shit! Oh my God!” The video pans to a laptop with bullet holes punched through its screen.

In another video, students are seen crouched and sheltering in the back of a classroom when a SWAT team enter, guns pointing directly at them. The students raise shaking hands in the air as bright police flashlights shine into their eyes. “Put your phones away! Put your phones away!” an officer orders.

Milan said her friend covered herself with a body on the first floor of the school’s freshman building. “She’s being used as a witness and her clothes are being used as evidence,” Milan said.

“‘I almost died, I got grazed, thank God I covered myself with someone’s body. I’m traumatized,’” Milan quoted her friend as saying.

Geovanni Vilsant, 15, told the Miami Herald he fled the school when he heard the gunshots and saw the bloody bodies of three people on the floor as he ran.

“There was blood everywhere,” he told the Herald. “They weren’t moving.”

Sheriff Israel told reporters authorities found “disturbing” social media posts linked to Cruz, a former student. Teachers and students described him as troubled.

“Girls thought he was creepy and weird,” Milan Parodie told The Daily Beast. “He wore a lot of black and was always alone... I don’t know how to put it but, like, he never seemed depressed or sad. He was always a little crazy is the best way to put it.”

Math teacher Jim Gard told the Miami Herald: “There were problems with him last year threatening students, and I guess he was asked to leave campus.”

Lisa Timitrakmis’s daughter Jayden Broome is a freshman and said she was in the band room when they went into lockdown. The fire alarm erupted, Timitrakmis told The Daily Beast, and then someone started yelling, “Code red, code red!” Broome could hear SWAT clearing the building, Timitrakmis added.

Student Nicholas Furatta was outside of the building when he heard five gunshots and ran, his father told The Daily Beast, adding, “We never thought it would happen in a place like Parkland.”

Parents rushed from work to pick up their children. One man yelled on his cellphone, “I don’t give a fuck about the customers right now, I need to know if he’s OK!”

Other parents were crying, somberly walking up to police officers and asking for any information on their children. Every other person said their phone or their child’s phone was about to die. Texts couldn’t get through and calls were dropped as everyone dug for any tidbit on their children.

Outside the high school, parents formed prayer circles. One mother broke down after finally getting to hear her daughter’s voice. “I’m so happy you’re OK,” she said.

Sheriff Israel told a press briefing late Wednesday that a football coach was among the dead and that a sheriff’s son was wounded.

President Trump tweeted his “prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school.” The White House canceled its daily briefing in response to the shooting.

The Parkland shooting is the 59th shooting at or near schools this academic year, according to Everytown, the gun control advocacy group.

“I have seen videos of school shootings before and I’ve heard about it,” Milan said “I never thought it would happen to my school, I always thought I was protected.”