A 19-year-old returned to the high school which had ousted him for indiscipline in the US state of Florida and went on a shooting spree, slaughtering 17 students and teachers in one of the 10 deadliest mass shootings in modern US history.
The teenager gunned down the victims with a semi-automatic AR-15 rifle -- first outside and then inside the Marjory Stoneman Douglas High School in Parkland on Wednesday afternoon, leaving the US in mourning.
Cruz, expelled from the school for "disciplinary reasons", kept firing as proceeded down the hallways, targeting frightened students and teachers even as they were scurrying for cover. He activated a fire alarm, sending people outside unaware of what was to come, officials said.
Students huddled in their classrooms used their phones to share then ongoing massacre on social media. Footage showed sprawled bodies, screams and gunfire which began with a few shots and then seemed to go on and on.
Beyond the bodies and blood lay piles of backpacks and dropped cell phones, some still ringing as desperate parents tried to reach their children.
Students recalled terror and confusion in the aftermath of the shooting.
"We had a fire drill early in the day, so we really didn't know what was going on," said Ryan Kadel, a 17-year-old.
"We went outside and we saw a security guard on a golf cart driving really fast and yelling at us to run."
"A lot of kids threw jokes around Iike that, saying that he's the one to shoot up the school, but it turns out everyone predicted it. It's crazy," one student recalled.
Law enforcement officials discovered "very, very disturbing" material on Cruz's social media accounts. His Instagram account showed several photos of guns. One appeared to show a gun's holographic laser sight pointed at a neighbourhood street. Another showed six rifles and handguns.
Jim Gard, who was Cruz's maths teacher at the school in 2016, said after the shooting that he learned from several students that Cruz was obsessed with a girl at the school to the point of stalking her, the Washington Post reported.
His adoptive mother -- her cousin Lynda Cruz -- died in November of pneumonia while his father passed away years ago.
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