Video report by ITV News Washington Correspondent Robert Moore
Florida shooting suspect Nikolas Cruz's defence lawyer has said her client is "sad" and "remorseful" - as a police report claimed he has confessed to the Valentine's Day gun massacre.
Melisa McNeill, who put her arm around Cruz as he appeared in court, told reporters the 19-year-old was a "broken human being" following the attack which killed 17 and injured at least 15.
A Broward County Sheriff's Office report said expelled ex-pupil Cruz confessed to being the shooter at Marjory Stoneman Douglas High School in Parklands.
The report claimed Cruz confirmed he "began shooting students that he saw in the hallways and on school grounds" then took off his rifle and vest so he could escape through the crowd.
Tom Bradby examines why massacres won't change America
Cruz appeared in court charged with 17 counts of premeditated murder.
"You’re charged with some very serious crimes," magistrate judge Kim Theresa Mollica told the suspected shooter, whose defence provided no argument.
The FBI has meanwhile confirmed it its investigating its handling of an apparent online threat the suspect is claimed to have made online last year
Law enforcement officials were tipped off about a comment on a YouTube channel last year, which read: "I'm going to be a professional school shooter."
Officials said officers carried out background checks but said they found "no indication of time, location or the true identity of the person who made the comment" and did not act further on it.
US President Donald Trump earlier pledged to take actions that "actually make (a) difference" to make America's schools safer after the nation's 18th school shooting in 2018.
Mr Trump said his administration would "tackle the difficult issue of mental health" but made no reference to changes in gun laws.
Former US President Barack Obama, a long-time advocate of gun reform, issued another call for "common-sense gun safety laws" shortly after Mr Trump spoke to the nation.
Mr Trump said he was "making plans to visit Parkland to meet families and local officials" and "continue coordinating the federal response" to the killings in Parkland, around 40 miles north of Miami.
In a TV address which he partly directed to "America's children", Mr Trump said: "You are never alone and you never will be."
The presidential speech from the White House came minutes after officials in Florida called for tightening to gun controls in a shared news conference.
State governor Rick Scott said he would speak to state leaders about making sure "individuals with mental illness do not touch a gun".
Sheriff Scott Israel added: "This community is hurting right now … I’m going to be very animated about what I think this country can do to possibly prevent these types of tragedies in the future."
"People are going to be rightfully so concerned about their rights. As am I.
"But what about the rights of these students? What about the rights of young kids? ... Don’t they have the right to be protected by the United States government to the best of our ability?”
Local superintendent Ron Runcie said students had urged him to demand change.
"Students have been reaching out to me, reaching out to staff, probably board members and others to say that now, now is the time for this country to have a real conversation on sensible gun control laws in this country," he said.
"Our students are asking for that kind of conversation," he added. "We can get it done in this generation, but if we don’t they will."
What happened in Nikolas Cruz's attack?
Officers said Cruz was equipped with an AR-15 rifle and that the attack began outside the building around 2.30pm local time on Wednesday.
Just before the shooting broke out the fire alarm sounded, with many students thinking they were having their second fire drill of the day.
As student filed out into the hallways, police say Cruz, equipped with a gas mask, smoke grenades and multiple magazines of ammunition, opened fire with a semi-automatic weapon
It was the nation's deadliest school shooting since a gunman attacked an elementary school in Newtown, Connecticut, more than five years ago.
Sheriff Scott Israel said Cruz was arrested without incident after he was located off the school grounds.
Footage later emerged of the arrest, with a man in a burgundy shirt bungled into a police vehicle before taken to a station.
Twelve of the victims have been identified as being from the school, the sheriff said.
This is believed to be the 18th shooting at a US school this year.
The moment the suspect was arrested
Sheriff Israel several SWAT teams were deployed during the afternoon and cleared every building at the school complex to ensure there were no other threats.
The FBI were called in to a scene which he described as "horrific".
Two students at the school told Good Morning Britain that the incident had not come as a surprise, describing the suspected attacker as "not a good kid".
"Ever since middle school he has always been very violent - just not in the right state of mind," Alaina Cruz said.
"He used to break things around the school just for the fun of it. He was not a good kid."
Sheriff Israel said of him: "We already began to dissect his websites and the things on social media that he was on and some of the things that came to mind are very, very disturbing."
Another student, Chad Williams, 18, said: "He was crazy about guns.
"He was kind of an outcast. He didn't have many friends. He would do anything crazy for a laugh, but he was trouble."
Who has led the repeat calls for tighter gun control?
In the wake of the attack a number of celebrities called for tighter gun controls in the US, including Kim Kardashian and Julianne Moore.
Boogie Nights actress Moore tweeted: "The 18th school shooting in the US since January. It is heartbreaking. What will it take to change our nation's gun laws ???"
Kardashian West said: "We owe it to our children and our teachers to keep them safe while at school. Prayers won't do this: action will. Congress, please do your job and protect Americans from senseless gun violence."
Singer Nancy Sinatra called on the Republican Party to pass "sensible" gun laws immediately.
"Seventeen more of our young people dead, killed by a shooter with an automatic weapon he had no business having," she added.
Talk show host Ellen DeGeneres said: "No words, no actions, no laws are enough until we end this epidemic of school shootings in our country."