What to Know
NBC 6 captured Nikolas Cruz being taken into jail just before 6 a.m., where he was later charged with 17 counts of premeditated murder.
Cruz was captured by officers less than an hour after he allegedly brought a weapon – believed to be an AR-15 – into the Parkland school.
In addition to the 17 fatalities, more patients remain at hospitals across Broward County – including five in critical condition.
President Donald Trump struck a solemn tone Thursday after the deadly school shooting in Florida, saying that the suspect had created a "scene of terrible violence, hatred and evil" and promising to "tackle the difficult issue of mental health," but avoiding any mention of guns.
Taking up the now-familiar ritual of public consolation after terrible violence, Trump spoke from the White House Diplomatic Room. In a slow, deliberate style, he sought to reassure a troubled nation as well as students' families and shooting survivors in Florida.
"We are all joined together as one American family, and your suffering is our burden also," Trump said. "No child, no teacher, should ever be in danger in an American school."
The president's address came a day after a former student opened fire at the Parkland, Florida, high school with an AR-15 rifle, killing 17 people and injuring 14 more. It was the nation's deadliest school shooting since a gunman attacked an elementary school in Newtown, Connecticut, more than five years ago.
At the Capitol, the usual divisions over gun laws were evident.
House Minority Leader Nancy Pelosi, a California Democrat, said in a statement that it is time for action. "Congress has a moral responsibility to take common-sense action to prevent the daily tragedy of gun violence in communities across America," she said. "Enough is enough."
Senate Majority Leader Mitch McConnell, a Republican from Kentucky, did not mention guns as he said the Senate would observe a moment of silence at noon. "To say that such brutal, pointless violence is unconscionable is an understatement," he said.
Former President Barack Obama called, as he often did after mass shootings during his presideny, for "common common-sense gun safety laws that most Americans want."
Before he was a candidate, Trump at one point favored some stricter gun restrictions. However, early in his administration, he told the National Rifle Association he was their "friend and champion." He signed a resolution passed by the GOP-led Congress blocking an Obama-era rule designed to keep guns out of the hands of certain mentally disabled people.
Trump, who owns a private club in Palm Beach, Florida about 40 miles from Parkland, said Thursday he was making plans to visit the grieving community. He praised teachers and first responders and also offered a direct message to children.
"I want you to know that you are never alone and you never will be," Trump said. "You have people who care about you who love you and who will do anything at all to protect you. If you need help, turn to a teacher, a family member, a local police officer or a faith leader. Answer hate with love, answer cruelty with kindness."
Trump pledged that his administration would work with state and local officials on improving school safety, saying: "It is not enough to simply take actions that make us feel like we are making a difference, we must actually make that difference."
Trump, who did not speak publicly immediately after the shooting, weighed in on Twitter early Thursday, calling the suspect "mentally disturbed" and stressing it was important to "report such instances to authorities, again and again!" He tweeted about the shooting twice on Wednesday, expressing condolences and saying he spoke with Florida's governor, who also avoided directly discussing gun control in his own remarks Thursday.
The president also issued a proclamation mourning the victims and ordering American flags at public buildings across the country flown at half-staff.
Parkland Mayor Christine Hunschofsky reacted to Trump's tweet in an interview on MSNBC, saying it's not clear what police can do if someone doing something suspicious hasn't done anything wrong.
"That's great, if you see something, you say something," she said. "I don't know what the police are able to do if you tell them there is somebody who has suspicious behavior but they haven’t done anything yet."
Hunschofsky also wanted to keep attention on "the people who really need our help right now" rather then getting "so caught up in politicizing debates, one way or another."
Trump has offered consolation before after horrific violence. A mass shooting in Las Vegas last year was the deadliest in modern history, with a gunman killing 58 people and injuring hundreds more, before killing himself. And a shooting in a Texas church in November left more than two dozen dead.
He has largely focused on mental health as a cause for mass shootings, dismissing questions about gun control.
After the Texas church shooting, the president said, "This isn't a guns situation." When he visited Las Vegas to mourn with the families of those victims, Trump called the shooter "demented" and a "very sick individual," though he added that "we'll be talking about gun laws as time goes by."
The 19-year-old suspect, Nikolas Cruz, is a troubled teenager who posted disturbing material on social media. He had been expelled from Marjory Stoneman Douglas High School for "disciplinary reasons," Broward County, Florida, Sheriff Scott Israel said.
Mayor Beam Furr said on CNN that the shooter was getting treatment at a mental health clinic for a while, but that he hadn't been back to the clinic for more than a year.
The extent to which Cruz was under investigation before the shooting is unclear.
Buzzfeed reported that the FBI was warned that a YouTube user named Nikolas Cruz commented on a video that he is "going to be a professional school shooter." But an FBI special agent said at a news conference Thursday that it is still not clear if they are the same person.
Melissa Falkowski, a journalism teacher at Douglas High School who hid her students in a closet during the shooting, said on MSNBC Wednesday night that she followed active shooter training protocol, but despite that, "we still have 17 casualties, 17 people that aren't going to return their families."
She said that was unacceptable, and called on the government to address such shootings. "From my personal viewpoint, it's time for Congress, the government, somebody to do something and its' time to talk about what the problem is and to try to fix it," Falkowski said.
NBC's Liz Lane and Asher Klein contributed to this report.