Here is a running summary of Wednesday's tragic shooting:

At least 17 killed, more than 20 injured

19-year-old suspect arrested and identified as Nicolas de Jesus Cruz, a aformer student who was expelled.

Teachers had been warned not to let Cruz onto campus with a backpack, and he had previously been the subject of schoolwide warnings about possible violence; last year he was not allowed to come back on campus because of threats against students.

It's not clear why he left the school

The town of Parkland is about 45 miles north of Miami

Sheriff said the total won't be known until the SWAT team gives the "all clear" - the school is still considered an active crime scene

The sheriff said that the suspect had "countless magazines" and was believed to have used an AR-15 rifle, used in previously mass shooting incidents including Newtown, Aurora and San Bernardino

One twitter user estimated that, since the Columbine High School shooting on April 20, 1999, more than 150,000 US students have been directly affected by school shootings

Cruz reportedly followed numerous gun groups as well as resistance groups on social media including the Syrian resistance & Iraqi fighters.

#Parkland shooting suspect Cruz followed all types of gun groups as well as resistance groups on social media including the Syrian resistance & Iraqi fighters. Cruz apparently was told last year he was not allowed to come back on campus because of threats against students. pic.twitter.com/vVEUlU72Sp — Nick Short 🇺🇸 (@PoliticalShort) February 14, 2018

Video of the school shooting suspect, still wearing his hospital gown, being escorted into Broward County Sheriff's headquarters

MOMENTS AGO: School shooting suspect escorted into BSO headquarters, still wearing hospital gownpic.twitter.com/vBZVVDfYRP — Breaking911 (@Breaking911) February 14, 2018

In another briefing, Sheriff Israel said the shooting "Started outside the school and went inside". Two succumbed to their wounds at the hospital, but it's unclear what state the scene is in. Twelve were killed inside the school, two were killed on a street outside, and two more succumbed to their wounds. It's unclear what happened to the 17.

Cruz is a legal adult and can be charged as such. At this point, it's unclear if Cruz is cooperating with police.

His arraignment will in all likelihood be tomorrow morning in Broward County State Court.

One expert said that Cruz may have legally purchased his firearm in the state of Florida where, despite warnings about his behavior, he wouldn't have been disqualified for mental health reasons.

It's unclear how Cruz acquired his weapon.

What is clear is that the gunman's behavior had been anticipated by his peers.

"Everyone predicted it," a student said about the #Parkland shooting. pic.twitter.com/mbzBIw8iUa — Vic Micolucci WJXT (@WJXTvic) February 14, 2018

Trevor Hart, 16, who knew Cruz in Spanish class, said Cruz had a bunch of weapons because Cruz talked about shooting lizards, squirrels and frogs. He said he thought he seemed “a little off.”

Cruz was taken into custody off campus without incident, he said. Wearing a red shirt, black pants and black boots, Cruz was seen being placed on a gurney. At 4:47 p.m. he was seen being wheeled into Broward Health North hospital in Deerfield Beach. Later he was taken from the hospital to Broward Sheriff’s Office headquarters in Fort Lauderdale.

Sixteen people were being treated at area hospitals. Seven victims were being treated at Broward Health Medical Center in Fort Lauderdale, Dr. Benny Menendez told a crowd of reporters. Two were in critical condition and five were stable. Nine were taken to Broward Health North Medical Center, where three were in critical condition.

“We do drills and when this happens we’re ready,” Menendez said. “We practice for this.”

At around dismissal time at 2:40 p.m., staff and students heard what sounded like gunfire and enacted a “code red” lock down, according to the Broward School District.

“It’s a horrific situation,” Broward County Superintendent Robert Runcie said. “It’s just a horrible day for us.”

Students were streaming down Pine Island Road at 3:30. Some of them crying, some talking on cell phones.

Meghan Walton's mascara was running as she walked down Pine Island Road with her mother. Derval Walton. She was waiting in the car line to pick her 15 year old freshman daughter up when she got the ominous text from her: "Code Red"

"Kids were running out full of blood," Derval Walton said. "Kids were falling in the grass."

Hannah Siren, 14, was in math class on the third floor.

"The people next door to us must have not locked their door," she said, breaking into tears. "They all got shot"

How many?

"10 or ... 7"

The following Twitter video captures the chilling sounds of the AR15 shooting right next to this Florida classroom.

chilling sounds of AR15 in classroom in Florida. former student 19 year old Nikolas Cruz taking out his rage. at least 17 dead, many in the hospital. 18th school shooting in U.S. this year. Shameful. on and for all of us.

Video Credit: Matt Walker/Snapchat pic.twitter.com/2ryCILI8Qa — Bill Ritter (@billritter7) February 15, 2018

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Watch a live feed of the coverage below:

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Update (6:00 pm ET): ABC is now reporting that at least 15 students were killed in today's attack, the number is expected to grow.

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Update (5:20 pm ET): A picture of the casualties from today's shooting is beginning to emerge.

There were at least 20 students injured in the attack; several are dead.

The shooter has been identified as an 19-year-old former student named Nicolas de Jesus Cruz.

According to Reuters, Cruz surrendered quietly.

Deputies arrested him in the Wyndham Lakes community in Coral Springs, just before 4 pm, a little over a mile away from the school, and a little over an hour after he fired his first shots, according to a local TV station...

“He was taken into arrest without incident,” said Broward County Sheriff Scott Israel.

"There was a time when he did attend the school," Israel said. "I don’t know why he left, I don’t know when he left."

A teacher at the school told the Miami Herald that Cruz, 19, had been identified as a potential threat to fellow students in the past. Emails had reportedly been sent warning teachers that the student had made threats against other in the past and that he should not be allowed on the campus with a backpack.

Another student interviewed on the scene by Channel 7 said Cruz had guns at home.

"We were told last year that he wasn’t allowed on campus with a backpack on him," said math teacher Jim Gard, who said the former student suspected in the shootings had been in his class last year. "There were problems with him last year threatening students, and I guess he was asked to leave campus."

One student told CNN that the school had recently held a meeting to discuss what to do in such an attack...

In his first public statement, Israel said "we have multiple casualties" and "there are folks who have lost their lives.."

Broward County Sheriff: "We have multiple casualties...there are folks that have lost their lives." pic.twitter.com/jyFfuUEodC — Breaking911 (@Breaking911) February 14, 2018

Police said they won't know the total toll of the attack until the SWAT team gives the all-clear...

"We don’t know if there are injured people," said Israel. "We don’t know if there are people hiding. We will not begin to open up the crime scene until the SWAT components say, ‘The school is safe and clear.’ When I hear all-clear, we’ll begin the next phase of this investigation."

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Dozens of victims are being reported in a shooting at Marjory Stoneman Douglas High School in Parkland Florida, a large high school with several thousand students, with authorities saying the gunman is now in custody...but the scene is still considered active.

Contrary to initial reports that there could be dozens of victims, NBC is reporting that 14 students have been shot.

The suspect's name has yet to be released. But reporters said he had previously attended the school, but wasn't currently enrolled...he's said to be 18 years old.

Suspect had previously attended the school but wasn't a current student and he was taken into custody without incident, according to @browardsheriff. — Steve Herman (@W7VOA) February 14, 2018

The suspect reportedly barricaded himself indoors before being taken into custody, footage of the suspect being taken into custody can be seen below...

The suspect matched the initial description of the suspect...

LATEST: There's been a school shooting at Douglas High School in Parkland, South Florida



- Sheriff confirms at least 14 victims

- Shooter is now in custody

- Police say scene 'still active' pic.twitter.com/Xr5SSCgUfq — MSNBC (@MSNBC) February 14, 2018

Florida Sen. Bill Nelson told MSNBC that there were "many" fatalities...

MANY DEATHS: Florida Sen. Bill Nelson told Fox News "there are many deaths" in the high school shooting in Parkland. #PrayForParkland — Breaking911 (@Breaking911) February 14, 2018

BREAKING: Broward Sheriff's Office: At least 14 victims in Florida school shooting, and "victims have been and continue to be transported to Broward Health Medical Center and Broward Health North hospital." https://t.co/Llzz7VjwCd — NBC News (@NBCNews) February 14, 2018

The shooting reportedly took place in a part of the building where freshman classes are typically held, one student told NBC.

PARKLAND SHOOTING SUSPECT IS NOW IN POLICE CUSTODY: WSVN7 — Jeff Lewis (@ChicagoPhotoSho) February 14, 2018

The Superintendent of Schools called it a "horrific situation".

“It’s a horrific situation”. School superintendent in Broward county. “Pray for these children and these families” pic.twitter.com/bGHdk32TWT — Doug Dunbar (@cbs11doug) February 14, 2018

One of the school’s students, caught up in the shooting, posted pictures from a classroom where he and his fellow students were hiding behind desks.

Still locked in. I checked the local news and there is 20 victims. Long live Majory Stoneman Douglas High. pic.twitter.com/4kQMAlCBWt — Aidan (@TheCaptainAidan) February 14, 2018

The town is 50 miles north of Miami. As Bloomberg described it, the school is "a sprawling complex set on a tract in the South Florida community..."

Initial reports suggest there could be more than 50 victims and said it's being treated as a "mass casualty" event. According to NBC, the suspect was described as a white male last seen leaving campus in a burgundy shirt.

President Trump tweeted that he "just spoke" to Fla. Gov. Rick Scott...

My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school. — Donald J. Trump (@realDonaldTrump) February 14, 2018

Just spoke to Governor Rick Scott. We are working closely with law enforcement on the terrible Florida school shooting. — Donald J. Trump (@realDonaldTrump) February 14, 2018

Police saying more than 20 people injured in active shooting situation at Marjory Stoneman Douglas High. @wsvn — Brian Entin (@BrianEntin) February 14, 2018

Perimeter set up around school. Some parents having a hard time getting close to Marjory Stoneman Douglas. Police have brought in armored vehicles. @wsvn — Brian Entin (@BrianEntin) February 14, 2018

#BREAKING BSO will be on scene to respond to media inquires. https://t.co/Bc3TVUcuHF — Coral Springs Police (@CoralSpringsPD) February 14, 2018

Aerial footage from CNN affiliate WSVN showed a number of people lying on the ground outside the school and being moved to ambulances. Dozens of police vehicles and ambulances are on site, including one tank, along with a team of heavily armed law enforcement officers as students ran or walked out. Some reported victims were seen being carried out of the school.

Coral Springs Police tweeted that students and teachers should remain barricaded inside the school until officers can reach them. People should stay away from the school due to an active police scene, police said. They also said that parents in touch with their students should refrain from calling 911.

The shooting went on for "some time..."

Television footage, seen below, showed police in fatigues entering the school with weapons drawn...then dozens of children frantically running and walking quickly out.

Students with hands up being brought out of school. Gunman still at large, preliminary reports up to 50 victims #breaking #CBSLA #StonemanShooting pic.twitter.com/RztdbcKLXs — Sandra Mitchell (@CBSLAsandra) February 14, 2018

Horrifying stories from students who were at the school are starting to trickle in...

Nicole Baltzer, 18, said she was in trigonometry class about 10 minutes before the end of the school day when the fire alarm went off. As students evacuated, she heard six gunshots and everyone started running back inside the school, according to CNN.

Dozens of law enforcement vehicles are on site, including one tank, along with a team of heavily armed law enforcement officers.

"I heard so many gunshots, at least like six. They were very close," Baltzer said.

Baltzer said she is still on lockdown in a classroom on the second floor. Her stepsister is also on lockdown in a different classroom, she said.

"Everyone just started freaking out," one student said.

According to Buzzfeed, a male student, who was not identified, told WSVN that he was on the campus at the time of the shooting.

He and other students near him heard an alarm go off, he said, and initially they thought the school was staging some sort of drill. Then they heard gun shots. "We heard pops," the student said, "and from the other side of the school we see the whole school running out."

One student posted video of students ducking for cover while the sound of gunshots could be heard in the background...

NEW: (WARNING-graphic scene) Cell phone video that was taken inside a classroom shows students hiding for cover while gunshots are heard in the background pic.twitter.com/FgmQRW18xH — CBS This Morning (@CBSThisMorning) February 14, 2018

Some students tweeted photos of them hiding under their desks...

My school is being shot up and I am locked inside. I’m fucking scared right now. pic.twitter.com/mjiEmPvGNb — Aj22000 (@TheCaptainAidan) February 14, 2018

Still locked in. I checked the local news and there is 20 victims. Long live Majory Stoneman Douglas High. pic.twitter.com/4kQMAlCBWt — Aj22000 (@TheCaptainAidan) February 14, 2018

Several agencies are responding to the incident, including the ATF and the FBI.

BREAKING: ATF agents from the Miami Field Division are responding to reports of a school shooting at Marjory Stoneman Douglas High School in Parkland, Fla. The investigation is ongoing and active. pic.twitter.com/7Wv93xMl2c — ATF HQ (@ATFHQ) February 14, 2018

Footage of students marching outside of the school with their hands up were taken by aerial cameras.

No information has been provided yet to parents, one parent told Bloomberg. "I'm scared for the other parents here. You can see the concern in everybody's faces. Everybody is asking, 'Have you heard from your child yet?'" one parent said.

As one twitter account pointed out, this is the eighteenth school shooting in the US so far this year....