'This is unbelievably catastrophic' – Shooter thought to be 18-year-old former student

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"This is unbelievably catastrophic," is how Broward County Florida Sheriff Scott Israel described the shooting scene at a Florida high school. 

There are multiple dead and injured after the violent incident today at Marjory Stoneman Douglas High School in Parkland, US. 

"I'm sick to my stomach," Mr Israel said to US ABC today. 

"There are folks who have lost their lives."

He could not confirm how many are dead, but could say it was more than one. 

The suspected shooter was found off campus, with reports he blended into fleeing students to escape to a nearby suburb where he was captured by police. 

Mr Israel said the was thought to be 18-year-old and attended the high school but was not a current student.