Authorities in southern Florida have charged a 19-year-old man with 17 counts of premeditated murder in connection with the latest mass shooting at a U.S. school.
Police arrested Nikolas Cruz after the attack Wednesday at Marjory Stoneman Douglas High School in Parkland, about 70 kilometers north of Miami.
They said he was a former student there who began firing outside of the school and continued to shoot inside the building before eventually blending in with a group of students as they fled.
In addition to the 17 deaths authorities reported as of late Wednesday, the shooting left others hospitalized.
Broward County Sheriff Scott Israel called the attack a "horrific, homicidal, detestable act."
Israel told reporters the shooter was armed with an AR-15 rifle and multiple ammunition magazines, and that the victims included both children and adults.
"I'm absolutely sick to my stomach to see children who go to school armed with backpacks and pencils lose their lives," Israel said. "This nation, we need to see something and say something. If we see different behavior, aberrant behavior, we need to report it to local authorities."
As an investigation into the violence continued Thursday new details emerged about the shooter from students and teachers who knew him.
'Disturbing' online activity
Investigators looking into Cruz's online activity, including his social media accounts, turned up what Israel described as "very disturbing" things. The county sheriff gave no details, but said Cruz had been expelled from the school for disciplinary reasons.
In a tweet Thursday morning, President Donald Trump said there were "so many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior. Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!"
The Associated Press cited a student who said Cruz was kicked out of the school after a fight with his ex-girlfriend's new boyfriend. He then enrolled at a different school.
The Miami Herald quoted a teacher at the school as saying Cruz threatened other students last year.
One student told reporters Cruz had a reputation in school of being "mentally unstable" and that he had threatened others.
"He was definitely not the kind of person who should have been allowed to have a gun," the student said.
The Orlando Sun Sentinel also reported that Cruz's mother died in November, leaving him in the care of a family friend where he was unhappy and subsequently went to live with another family that is cooperating with investigators.
Before going to a hospital to meet with victims and their families, Florida Governor Rick Scott gave his reaction to the attack, saying it was "absolutely pure evil."
"The first you think about is, you know, God I hope this never happens to my family. Then, you think about, you're furious," Scott said. "How could this ever happen in this country? How could this happen in this state? This is a state that is focused on keeping all of our children safe."
State will pay for funerals
The state's Attorney General Pam Bondi said Florida will pay for the funerals and counseling for the families. The local school system is also making grief counselors available for students.
Students told television networks Wednesday unfolded like a normal day of school until a fire alarm sounded. They said they then heard gunshots, sending the students either running from the building or trying to hide.
Video taken inside a classroom showed students crouched under desks, screaming in shock and terror while gunshots sounded. Other students hid in closets, using their cellphones to text emergency messages to their parents.
President Trump offered Florida authorities all the federal help they need and tweeted his "prayers and condolences" to the victims and their families. "No child, teacher or anyone else should ever feel unsafe in an American school," he said.
Prior mass shootings have brought calls for tighter gun controls in the United States. Trump said after a November attack at a Texas church that stricter laws would not have stopped that gunman.
Senator urges concrete action
Democratic Senator Chris Murphy of Connecticut was among those Wednesday who urged more concrete action, blaming Congress for what he called a "scourge" of school shootings.
"It only happens here, not because of coincidence, not because of bad luck, but as a consequence of our inaction. We are responsible for a level of mass-atrocity that happens in this country with zero parallel anywhere else," Murphy said.
He added on Twitter, "If you're a political leader doing nothing about this slaughter, you're an accomplice."
Connecticut is home to Sandy Hook Elementary School in Newtown, where 20 elementary school children and six adults were massacred in a 2012 shooting.
Mike Bowman contributed to this report