What you should know about the South Florida school shooting

JACKSONVILLE, Fla. – At least 17 people are dead following a school shooting Wednesday at Marjory Stoneman Douglas High in Parkland, Florida, authorities confirmed.

Broward County Sheriff Scott Israel said the suspected gunman, Nikolas Cruz, opened fire with an AR-15 rifle shortly before the school was set to dismiss students for the day.

Responding deputies were met with hundreds of students fleeing the school. Investigators later said they learned that he had concealed himself in the crowd and was among those running out of the school.

According to Broward Schools, Marjory Stoneman Douglas High will be closed for the rest of the week, and all school activities have been canceled. Westglades Middle School will be open for the rest of the week and grief counselors will be available at the school for students and staff.

READ: Message from superintendent of Broward County Public Schools

The Broward County Sheriff's Office held it's first media briefing Thursday morning around 10:30 a.m.

"Today is a day of healing. Today is a day of mourning,” said Sheriff Israel. 

They are now interviewing everyone who was at the high school on Wednesday, to see who may have information that could help with the investigation. The families of all 17 shooting victims have been notified, according to the sheriff. 

Since the shooting, Sheriff Israel reports there have been several copycat shooting threats made at other schools.

His warning to copycats: "We will respond to every threat, in full, and investigate it. Every call that's made that draws resources away from where they need to be, the full power of the sheriff's office will make sure the max charge comes down for doing something so horrific, so pathetic."

At the briefing, Broward School Superintendent Robert Runcie said grief counselors are available at several locations in Parkland and Coral Spring. Students have reached out to him and said that now is the time for the country to have a real conversation about sensible gun control measures. Runcie said the students deserve it, and if this generation won’t do it, theirs will.

A vigil was held Thursday afternoon for survivors in the shooting. A sunset vigil was also scheduled for 6 p.m.

Here's what we know right now:

Who is involved?

Cruz, 19, is a former student who was previously expelled from the school, Israel said. The sheriff said Cruz had multiple magazines in addition to the rifle. He was taken into custody without incident in a residential neighborhood about a mile away from the school. Cruz was booked into the Broward County jail early Thursday morning. According to the Broward County Sheriff's Office website, he has 17 counts of premeditated murder and will appear in court at 2 p.m. Thursday.

Authorities said the suspect was equipped with a gas mask and smoke grenades, and set off a fire alarm to draw students out of classrooms shortly before the day ended at one of the state's largest schools.

Israel said investigators are dissecting the suspect's social media posts and found material that is "very, very disturbing." But he did not elaborate.

FBI Agent, Rob Lasky also reported that the agency investigated a YouTube post last year where the user said,  “I’m going to be a professional school shooter.” No information was given on the time or location and they were not able to determine who made the comment.

RELATED: Florida school shooting suspect made 'disturbing' social media posts

An ex-schoolmate recalled Cruz posting on Instagram about killing animals and said he talked of doing target practice in his backyard with a pellet gun.

Student Daniel Huerfano, who escaped the shooting, told The Associated Press that he knew the suspect when he attended the school. Huerfano said he remembered seeing Cruz walking around the school with his lunch bag, adding, "He was that weird kid that you see ... like a loner."

School superintendent, Robert Runcie, told reporters he didn't know of any concerns raised about Cruz.

Sheriff Israel said that the AR-15 Cruz used was purchased legally about a year ago. There was an armed school security officer at the school during the shooter, but he never saw the shooter. 

How many casualties are there?

At a Wednesday evening news briefing, Sheriff Israel told reporters that 17 people- including a football coach, died as a result of the shooting. He said 12 people were killed inside the school, two outside, one on a nearby street and two others succumbed to their injuries at the hospital.

Later in the evening, Israel said that families of the dead are being notified. He said 12 of the dead have been identified. He said not all victims were carrying identification and thus couldn't be quickly identified.

The coach who was killed was not identified by the sheriff's office. However, the high school football team's Twitter account did send out the following post Thursday morning:

News4Jax's sister station in South Florida, WPLG also reported that Jamie Guttenberg died in the shooting. Her brother, Jesse, made it home, according to the report. 

Two of the victims, according to Superintendent Runcie, were members of the faculty who died as heroes trying to save students.

What are authorities saying?

President Donald Trump, Gov. Rick Scott, Sen. Bill Nelson and Jacksonville Mayor Lenny Curry are among the leaders who have offered their condolences in the wake of the shooting.

Thursday morning, the president spoke directly to schoolchildren, teachers and families across the country in the wake of the Florida school shooting, saying the nation is "in grief." He added that he will be visiting Parkland and continue to coordinate federal efforts. 

“Each person who was stolen from us yesterday had a full life ahead of them. Each one had dreams to pursue, love to give and talents to share with the world. And each one had a family to whom they meant everything in the world,” said Trump.

He also thanked law enforcement, teachers, and heroes who responded in the face of dange. He encouraged neighbors to come together and "answer hate with love". "“These bonds are stronger, the forces of hatred and evil and these bonds grow stronger in the hour of our greatest need.”

In honor and remembrance of the victims, Scott also directed United States and state of Florida flags to be flown at half-staff at all local and state buildings, installations and grounds throughout the state until sunset on Monday, Feb. 19.

On Wednesday night, Scott joined law enforcement agents near the site of the deadly school shooting and offered his condolences to the victims' families and survivors. He said the attack that claimed at least 17 lives "is just absolutely pure evil." and wants to make sure this never happens again.

“The violence has to stop. We cannot lose another child in this country to violence in a school,” said Scott.

During Thursday's briefing, the governor stated that he will be meeting with state leaders to discuss two key points: how to ensure everything is being done to make sure students are safe in schools, and making sure individuals with mental illnesses can't access a gun. 

Florida Attorney General Pam Bondi said the state will cover funeral expenses for the victims and counseling for survivors.

Sen. Marco Rubio also released a statement early Wednesday evening:

“A mass shooting at one of Florida’s schools is a day you pray will never come. Jeanette and I are devastated and saddened by today’s inexplicable tragedy at Broward County’s Marjory Stoneman Douglas High School. We join millions of Americans in praying for the victims, their families and all the students and teachers impacted by today’s events. We are grateful to the emergency responders, law enforcement officials, nurses and doctors who assisted the victims of today’s tragedy. Over the next few hours and days we will learn more about why and how this killer carried out this carnage. My office and I remain ready to assist state and local officials and anyone impacted by this horrible tragedy.”

Numbers, websites to know

HOW TO HELP: OneBlood needs O-negative blood donations after Florida school shooting

GoFundMe: Stoneman Douglas Victims' Fund