A teenager has been charged with 17 counts of premeditated murder after yesterday's mass shooting at a high school in Florida.
19-year-old Nikolas Cruz is accused of opening fire at his former school in Florida.
US Police are still trying to establish a motive for the attack.
Police say they are beginning to "dissect" Mr Cruz's internet and social media use – with Broward County Sheriff Scott Israel describing some of the things he had already become aware of as "very, very disturbing."
This photo provided by the Broward County Jail shows Nikolas Cruz, 14-02-2018. Image: AP/Press Association Images
Mr Cruz is accused of being the gunman who went into Marjory Stoneman Douglas High School in Parkland on Wednesday afternoon, armed with at least one AR-15 assault rifle, a gas mask, smoke grenades and several magazines of ammunition.
The gunman deliberately set off the fire alarm so youngsters would leave their classrooms as he arrived at the scene, about 45 miles north of Miami, Florida Senator Bill Nelson told CNN.
He then targeted pupils.
Twelve people were shot dead in the school building, two outside, one in the street and two people were left with injuries from which they later died.
The Ar-15 rifle is the same model used in mass-shootings at Las Vegas and Orlando.
This is America's 18th school shooting this year and third deadliest ever.
A law enforcement officer rushes toward Stoneman Douglas High School in Parkland, Florida, 14-02-2017. Image: Sun Sentinel/TNS/ABACA/ABACA/PA Images
Police said they were met with “hundreds of students fleeing the school” when they responded to reports of the attack.
Investigators later learned that the gunman had “concealed himself in the crowd and was among those running out of the school.”
Mr Cruz was identified as the suspect from school security footage. Police said he had attended and was expelled from the school the previous year.
He was detained without incident in the nearby town of Coral Springs and taken to hospital with minor injuries.
These students were inside:
In a statement, School Superintendent Robert W. Runcie said “There are no words to express the sorrow that we are all feeling.”
Today we experiencing the worst of humanity as an unspeakable tragedy has hit our @browardschools family at Marjory Stoneman Douglas HS. There has been a shooting on campus with injuries and fatalities. We are working with law enforcement as we pray for our babies and families.
— Supt Runcie (@RobertwRuncie) February 14, 2018
“Dealing with this tragedy is going to take time,” he said. “And we will be here for every student, every family and every staff member.”
“Our hearts are broken. Please keep everyone in your thoughts and prayers.”
US President Donald Trump also expressed his condolences to the families of the victims, adding “No child, teacher or anyone else should ever feel unsafe in an American school.”
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
Medical personnel tend to a victim outside of Stoneman Douglas High School in Parkland, Florida, 14-02-2018. Image: Sun Sentinel/TNS/ABACA/ABACA/PA
Among those who tried to save students was football coach Aaron Feis, who died after apparently using his body as a shield against the bullets.
Reports emerged soon after the shooting about Mr Feis' bravery with many current and ex-pupils hailing his actions.
One, who called herself Angelica Losada, posted a picture of the coach with a baby, adding: "This, ladies and gentlemen, (is) the face of a hero.
"Coach Aaron Feis was injured protecting a student in the shooting at Marjory Stoneman Douglas High School and, at last report, is in critical condition.
"He is a friend to all students that know him. He was always so nice to me when I went to school there, and I know he is close with my brother and his friends."
Rather than sharing details of the shooter, I choose to HONOR the bravery of HEROS like a Football Coach & security guard Aaron Feis. He stepped in front of students as shots were being fired. He took multiple bullets and later died. Aaron Fies, YOU ARE A HERO. pic.twitter.com/Y0czj16aSX
— Athletes In HS (@AthIetesInHS) February 15, 2018
Although he was initially reported to be critical, he was later believed to have died in hospital.
Florida Senator Marco Rubio of Florida said in a statement he hoped authorities could find out in coming hours and days more about why and how the killer "carried out this carnage."
Despite his former students saying there were warnings, authorities in Parkland appeared to claim there was nothing they could have done to prevent the attack.
Officials said Mr Cruz was a former student at the school, but was expelled for unspecified disciplinary reasons.
Victoria Olvera, a 17-year-old at Marjory Stoneman Douglas, says Mr Cruz was expelled last school year after a fight with his ex-girlfriend's new boyfriend.
Another former friend, Dakota Mutchler, said he hadn't seen him in more than a year after his expulsion before which "he started progressively getting a little more weird."
Chad Williams, an 18-year-old at the high school, remembered Mr Cruz as a troubled classmate from middle school.
He said Mr Cruz would set off the fire alarm, day after day, and finally got expelled in the eighth grade.
More recently, Mr Williams saw Mr Cruz carrying several publications about guns when they met by chance at the high school, where he thought Mr Cruz was picking up a younger sibling.
"He was crazy about guns," said Mr Williams. "He was kind of an outcast. He didn't have many friends. He would do anything crazy for a laugh, but he was trouble."
Maths teacher Jim Gard told the Miami Herald that Mr Cruz had been forbidden from bringing a backpack on to the campus.
"There were problems with him last year threatening students, and I guess he was asked to leave campus," Mr Gard told the newspaper.
Video has emerged that shows students cowering in a classroom as loud rapid shots are heard nearby.
McKenzie Hartley, 19, said her sister was inside the school at the time and she told Reuters: "She heard him shooting through the windows of classrooms and two students were shot."
Broward County Mayor Beam Furr told CNN that Mr Cruz had been getting treatment at a mental health clinic for a while, but had not been to the clinic for over a year.
"It wasn't like there wasn't concern for him," Mr Furr said.
"We try to keep our eyes out on those kids who aren't connected. Most teachers try to steer them toward some kind of connections. In this case, we didn't find a way to connect with this kid," he added.
Superintendent Runcie told reporters he did not have any warning.
Typically you see in these situations that there potentially could have been signs out there," he said. "I would be speculating at this point if there were, but we didn't have any warnings.
There weren't any phone calls or threats that we know of that were made."
Sheriff Israel said: "If a person is predisposed to commit such a horrific event by going to a school and shooting people... there's not anybody or not a lot law enforcement can do about it."
The injured were taken to two hospitals where at least three of them were critical and another three serious.
Authorities have embarked on a programme of counselling for anyone affected.
It is believed to be the second deadliest school shooting in US history, after Sandy Hook Elementary school in 2012, which left 28 dead.
Donald Trump tweeted: "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."
With reporting from IRN ...