PARKLAND, Fla. — A former student opened fire at a Florida high school Wednesday, killing at least 17 people and sending scores of students fleeing into the streets in the nation's deadliest school shooting since a gunman attacked an elementary school in Newtown, Connecticut.Frantic parents rushed to Marjory Stoneman Douglas High School to find SWAT team members and ambulances surrounding the campus as classes prepared to dismiss for the day. Live footage showed emergency workers who appeared to be treating the wounded on sidewalks."It is a horrific situation," said Robert Runcie, superintendent of the school district in Parkland, about an hour's drive north of Miami. "It is a horrible day for us."The 19-year-old suspect was taken into custody without a fight about an hour after he left the scene, authorities said.Broward County Sheriff Scott Israel said the suspect, who was previously expelled for disciplinary reasons, had at least one rifle and multiple magazines."It's catastrophic.