PARKLAND, Florida - A former student opened fire at a Florida high school Wednesday, killing at least 17 people, sending students running out into the streets and SWAT team members swarming in before authorities took him into custody about a mile away.

Sheriff Scott Israel identified the suspect as Nikolas Cruz, 19. A law enforcement source briefed on the shooting at Marjory Stoneman Douglas High School said the suspect appears to have pulled the school fire alarm, causing chaos, and then started shooting, reports CBS News senior investigative producer Pat Milton.

CBS News' Jeff Pegues reports the suspect had a AR-15-style weapon with multiple magazines on his person. Sources say that authorities are rushing to trace this weapon and its origin and how Cruz obtained it. Pegues says it well help investigators determine a timeline leading up to the attack.

Previously, Israel had said the shooter was a former student. He said the shooter was outside and inside the school at points during the attack, and taken into custody "without incident" about an hour after he left the school. Israel said police were waiting for the SWAT team to give them the all-clear so that they could go inside the school.

A male that fit the description of the suspect was seen being taken into custody, CBS News' Jeff Pegues reports. He was later transported to the hospital and seen being wheeled into the facility on a gurney.

Broward County Schools superintendent Robert Runcie said there were numerous fatalities, but couldn't confirm the number. He called it a "horrific situation."

Former classmate Eddie Bonilla told CBS Miami he knew Cruz before he got kicked out of school.

"He got kicked out of school last year," said Bonilla. "He always had guns on him and stuff like that."

He said he was not surprised by the arrest.

"Honestly a lot of people a lot of people were saying it was going to be him," Bonilla said. "We actually, a lot of kids threw jokes around Ike that, saying that he's the one to shoot up the school, but it turns out everyone predicted it. It's crazy."

Alex Azar told CBS Miami he remembers Cruz too.

"He always seemed like the unstable type, the type who would do this sort of thing," Azar remembers. "He was always in the office. He was always in trouble, very unstable. He had that look to him, kind of sinister."

School Superintendent Robert Runcie said there were no warnings that something like this would happen.

"We received no warnings," Runcie told reporters outside the school. "Potentially there could have been signs out there. But we didn't have any warning or phone calls or threats that were made."

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