A 19-year-old man who had been expelled from his Florida high school is being held on 17 counts of murder, suspected of unleashing one of the deadliest school shootings in US history.
On Wednesday Nikolas Cruz walked into the Marjory Stoneman Douglas High School in Parkland and opened fire on students and teachers, Broward County Sheriff Scott Israel said. Police believe he acted alone.
Cruz was armed with an AR-15-style rifle and had multiple ammunition magazines when he surrendered to officers in a nearby residential area, police said.
He loved guns and was expelled for unspecified disciplinary reasons, police said.
The shooting is the 18th in a US school this year, according to gun control group Everytown for Gun Safety.
It was the second deadliest shooting in a US public school after the 2012 massacre of 20 first-graders and six teachers at Sandy Hook Elementary in Newtown, Connecticut.
The deadliest school shooting in US history was at Virginia Tech in 2007, when 32 people were killed.
The Florida shootings stirred the long-simmering US debate on the right to bear arms, which are protected by the Second Amendment of the US Constitution.
Schools across the country have installed electronically secured doors and added security staff, but few legislative solutions have emerged.
"So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior," US President Donald Trump tweeted. "Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!"
Hundreds of panicked students fled the building, running past heavily armed, helmeted police officers while others huddled in closets.
Parents raced to the school of 3300 students and a nearby hotel that was set up as a checkpoint to find their children.
The assailant wore a gas mask as he stalked into the school carrying a rifle, ammunition cartridges and smoke grenades, then pulled a fire alarm, prompting students and staff to pour from classrooms into hallways, according to Florida's two US senators, who were brief by federal authorities.
Cruz had recently moved in with another family after his mother's death in November, according to Jim Lewis, a lawyer representing the family, bringing his AR-15 along with his other belongings.
The family believed Cruz was depressed, but attributed that to his mother's death, not mental illness.
"They didn't see any danger. They didn't see any kind of predilection this was going to happen," Lewis told CNN.
A chilling cell phone video broadcast by CBS News showed what it said was the shooting in progress from inside a classroom.
Several students were huddled or lying on the floor surrounded by mostly empty desks.
A rapid series of loud gunshots are heard along with hysterical screaming.