CORAL SPRINGS, Fla. -- Seventeen people were killed and multiple people were injured when a former student opened fire at Marjory Stoneman Douglas High School in Florida on Wednesday, prompting a massive police response and manhunt as frightened students hid in their classrooms. Police identified the suspect as Nikolas Cruz, 19, a former student who was taken into custody about an hour after shooting began.

"It's catastrophic, there really are no words," Broward County Sheriff Scott Israel said.

As of 9 p.m. ET, Israel said 12 of the 17 victims had been identified. Israel said they would not be providing the names of the victims until all of the families are notified. Israel said some of the students did not have their backpacks or identification on them.

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Israel said "we lost a football coach" in the shooting and a deputy sheriff's son had been shot.

Broward County School Superintendent Robert Runcie said the suspect was a former student of Marjory Stoneman Douglas High School and was currently enrolled in Broward County schools.

Runcie said there will be grief counseling for students and victims' families beginning early Thursday.

"We are going to pull through this as a community," Runcie said.

Police appear to take a man into custody outside Marjory Stoneman Douglas High in Parkland, Florida, on Wednesday, Feb. 14, 2018. WFOR-TV

A law enforcement source briefed on the shooting said the suspect appears to have pulled the school fire alarm, causing chaos, and then started shooting, reports CBS News news senior investigative producer Pat Milton.

Israel said the suspect used an AR-15 and had multiple magazines on him, CBS Miami reports.

The suspect was taken into custody without incident off campus, Israel said. He had been expelled for disciplinary reasons, and had at least one rifle and multiple magazines when he was taken into custody about an hour after the shooting started.

Broward Health North doctors said 9 patients, including the suspected gunman Nikolas Cruz, were taken to their facility, CBS Miami reports. Of the shooting victims, three are in critical condition, three are stable and two others have died.

At last check, three patients were in the operating room.

Cruz was seen being taken into custody before being placed on a stretcher and transported in an ambulance to the hospital. Doctors said he was treated and released to police.

On Wednesday night, Runcie called the shooting a "horrific situation."

"It's just a heartbreaking tragedy," Runcie said.

Runcie said the shooter entered the school during dismissal. Israel said the shooter was outside and inside the school at various times. Runcie said there was no warning or threats made before the incident.

Some of the current students told authorities they knew the suspect, Milton reports. Student Brandon Minoff, speaking with CBSN, said he had had classes with Cruz. Minoff described the suspect as a "strange kid."

Another student told CBS News about the suspect, "The kid was crazy. I had engineering with him a couple years ago and he wasn't allowed to come to school with a backpack and he would threaten students and break glass and get into fights so he got kicked out of school."

Ambulances converged on the scene as emergency workers appeared to be treating wounded people on the sidewalks.

Television footage showed police in olive fatigues, with weapons drawn, entering the Marjory Stoneman Douglas High School, then dozens of children frantically running and walking quickly out A police officer waved the students on, urging them to quickly evacuate the school.

Some students exited the building in single-file rows with hands raised overhead to show they carried no weapons. Others held onto other students as they made their way out past helmeted police in camouflage with weapons drawn.

Emergency medical personnel pulled stretchers from the backs of ambulances as police cars surrounded the parking lot. At least one person was seen being wheeled to the ambulance on a gurney.

Noah Parness, a 17-year-old junior, said the fire alarm went off for the second time of the day about 2:30 p.m. He said he and the other students calmly went outside to their fire drill areas when he suddenly heard several pops.

"Everyone was kind of just standing there calm, and then we saw a bunch of teachers running down the stairway, and then everybody shifted and broke into a sprint," Parness said. "I hopped a fence."

Student Jeiella Dodoo described a chaotic scene as students fled. She said she hurt her toe while jumping a fence. She heard from a friend that people were being loaded into ambulances.

NEW: Photo from a student in the school barricaded in a classroom at Marjory Stoneman Douglas High where an active shooter incident is underway pic.twitter.com/rBVrENjtCM — CBS Evening News (@CBSEveningNews) February 14, 2018

"That's when we knew it was really real, there was an actual shooter on campus," Dodoo told CBS News.

Parent Caesar Figueroa told CBS News his daughter was hiding in a closet and afraid to speak on the phone. He said they have been texting. The girl said she heard gunfire and the window blew, and she screamed and ran in the closet with her friend. She told Figueroa she heard everyone screaming and running.

She said three students were shot in the classroom next to her. She was no longer hearing gunfire, Figueroa said.

He said it was like a "war zone" with the police response.

"It's the worst nightmare not hearing from my daughter for 20 minutes, it was the longest 20 minutes of my life," Figeuroa said.

Another parent, Beth Feingold, says her daughter sent a text at 2:32 p.m. saying "We're on code red. I'm fine." But she then sent another text soon afterward saying, "Mom, I'm so scared." The girl was later able to escape the school unharmed.

Len Murray's 17-year-old son, a junior at the South Florida high school where shooting was reported, sent his parents a chilling text: "Mom and Dad, there have been shots fired on campus at school. There are police sirens outside. I'm in the auditorium and the doors are locked."

Those words came at 2:30 p.m. Wednesday. A few minutes later, he texted again: "I'm fine."

Murray raced to the school only to be stopped by authorities under a highway overpass within view of the school buildings in Parkland. No information was immediately given to parents, Len Murray said.

The sheriff later told parents to go to the Marriott in the Heron Bay complex, where students were being taken to be reunited with their families.

Murray said, "I'm scared for the other parents here. You can see the concern in everybody's faces. Everybody is asking, 'Have you hard from your child yet?'"

The FBI said it was on the scene and assisting local law enforcement. ATF agents from the Miami Field Division are also responding to the scene.

The White House said President Trump has been briefed on the shooting and is monitoring the situation. Mr. Trump expressed his condolences in a tweet Wednesday afternoon, saying that "no child, teacher or anyone else should ever feel unsafe in an American school."

This is a developing story and will be updated.