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Videos on social media show what students endured inside classrooms at Marjory Stoneman Douglas High School during and after a mass shooting.
Twitter user @Melody_Ball shared video she said was from her little brother.
It shows SWAT officers entering a classroom and telling students to put their hands up and phones away.
Gunshots can be heard on another video posted from inside a classroom.
The Broward County sheriff said 17 people were killed in the shooting at the Parkland, Florida, high school.
Deputies responded to the school after a fire alarm went off and gunshots rang out at approximately 2 p.m.
The suspect has been identified as former student Nikolas Cruz.
He was taken into custody off-campus after the shooting.
In a 9 p.m. briefing to the media, Broward County Sheriff Scott Israel announced 12 of the 17 victims were identified.
Florida Gov. Rick Scott was also in attendance.
"This is absolutely pure evil," said Scott. "This state does not tolerate violence -- we have law enforcement that will always show up to defend our safety."
Broward County Public Schools Superintendent Robert Runcie also spoke during the briefing.
"Today's shooter was a former Marjory Stoneman Douglas student and was currently enrolled in Broward County Public Schools," Superintendent Runcie said.
Parents were still showing up to a local Marriot hotel in Coral Springs to look for their children at almost 11:30 p.m. hours after the deadly shooting in Parkland.