"Attention please. Lockdown. Locks, lights, out of sight. Attention please. Lockdown. Locks, lights, out of sight. Attention please. Lockdown. Locks, lights, out of sight. "

"Attention please. Lockdown. Locks, lights, out of sight. " The automated announcement was the only sound repeatedly punctuating the silence in the pitch-black classroom where Lillian Duarte and her classmates spent 20 terrifying minutes on Tuesday afternoon.

The words were familiar to 15-year-old Duarte, who has participated in nearly 50 active shooter drills in the five years she's been a student at the STEM School in Highlands Ranch, Colorado, a few miles away from Columbine High School.

Only this time, it wasn't a drill. Two students opened fire on their classmates on Tuesday, killing one and injuring eight others before they were taken into custody.

Lillian Duerte Lillian Duarte

Duarte provided BuzzFeed News with minutes-long cellphone videos she took while hiding in her classroom and a series of frantic, frightened text messages she exchanged with her family and friends during the shooting.

The videos and text messages provide a horrifyingly familiar glimpse into what it's like for students hiding in their classrooms during a mass shooting. When Duarte, her math teacher, and around 35 of her classmates first heard the lockdown announcement over the school speakers, they were confused about whether it was a drill or an actual shooting, Duarte told BuzzFeed News on Wednesday. "The teacher paused for a second," Duarte said. "She wasn't sure whether to lock the door or not. Everyone thought it was a drill at the time." So Duarte and her classmates sat in clear view of the classroom door. Then Duarte got a text in her group chat from her friend in another classroom who had heard gunshots: "This is real. There's a shooter. I'm not kidding."

Duarte

"I just want to say I love you all if anything happens," Duarte texted her three other friends.

She later added, "Are the police here what's happening I'm so scared."

Duarte

"Whoever's doing it was in the room next to me," one of her friends wrote in the group chat. "He yelled I have a gun."

Duarte

Duarte, who was still in the clear view of the classroom door, texted her friends, "I feel so exposed where I'm sitting I feel it wouldn't be hard at all to kill me."

She then showed the texts from her friend to her teacher. They then turned off all the lights, took down the Christmas lights that were hanging in the classroom, and moved to the other end of the class, farther away from the door. "I started crying I'm so scared," Duarte told her friends.

Duarte

Duarte

That's when Duarte began messaging her parents and friends to tell them that she loved them.

"We were all just so worried we would die," she told BuzzFeed News.

Duarte

She also texted her 18-year-old sister, Vivian, to tell her she loved her.

Duarte

Duarte then recorded several minutes of the lockdown as she was crouched under her desk. You can hear shouting in the distance.

She continued to text with her friends in their group chat. "They're trying to get him now. The police," one of her friends who was near the shooting told the others. "I just heard someone yell freeze."

Duarte

Duarte recorded the moment her classroom door was kicked open by police officers. Even though they said they were police, Duarte thought the shooters had entered her classroom. She began crying.