A disturbing profile has been emerging a day after the horrific school shooting at Marjory Stoneman Douglas High School in Parkland, Florida, where 19-year-old suspected gunman, Nikolas Cruz, killed 17 people and injured another 20.
Cruz, a former student at the high school who was expelled for unspecified disciplinary reasons, set off a fire alarm to get students out of the classrooms on Wednesday, and opened fire with his AR-15 assault rifle through the halls.
Reports are emerging that the FBI had been warned months ago about his stated intent to carry out a school shooting, with teachers at the school and classmates also attesting that his attitude and online postings were cause for serious concern.
Unlike a number of other mass school shootings in the United States, Cruz was captured alive by police, and is being held in a secure location after being treated at a local hospital.
Here are five key things to know about 19-year-old suspected mass shooter.
1. FBI Agents Knew He Wanted to Be a School Shooter
Not only did Cruz make his intentions of being a school shooter known months ago, but FBI agents were reportedly investigating him.
NY Daily News reported that Ben Bennight, a bail bondsman in Mississippi, said he notified the FBI about comments Cruz made on YouTube in September, where the teenager said he wanted to be a "professional school shooter."
Bennight sent a screenshot of the comment to the FBI, with agents visiting him later that month to ask him for more information about Cruz.
The bondsman said that agents from Mississippi and Miami visited him at a later date after Cruz took an AR-15 to Marjory Stoneman Douglas High School.
"I would like to think that they were already investigating this guy and they had him on the top of their radar and that's how they ended up contacting me so quickly," Bennight said.
2. Teachers at the High School Were Warned Too
Classmates and teachers have said that it was no secret that Cruz was a troubled teenager, with some school staff admitting they were explicitly warned about the student.
Math teacher Jim Gard told the Miami News Herald that he had received an email from school administration about Cruz, who was one of his students.
"We were told last year that he wasn't allowed on campus with a backpack on him," said Gard, who had him in class. "There were problems with him last year threatening students, and I guess he was asked to leave campus."
Drew Fairchild, a Marjory Stoneman Douglas High student who had Cruz as a classmate in his freshman year, said that he "used to have weird, random outbursts, cursing at teachers."
Still, Superintendent Robert Runcie insisted that he was not aware of any concerns about Cruz.
"We received no warnings," Runcie claimed. "Potentially there could have been signs out there. But we didn't have any warning or phone calls or threats that were made."
3. Cruz Had an Obsession With Guns
Broward County Sheriff Scott Israel said investigators are analyzing Cruz's digital profile, and have found "very, very disturbing" content.
He posted photos of himself with various guns, often concealing his face, and made multiple threats on YouTube and other sites.
"I whana shoot people with my AR-15" (sic), "I wanna die Fighting killing [expletive] ton of people" and "I am going to kill law enforcement one day they go after the good people," were among some of the things he posted, according to CNN.
A U.S. official briefed on the investigation said Cruz had legally purchased his AR-15 style rifle and had passed the background checks needed for the purchase.
While it is not yet clear if and what kind of mental illness Cruz might be suffering from, Israel said: "While people who are the victim of mental health illnesses are being treated, in the opinion of this sheriff, they should not be able to buy, surround themselves, purchase or carry a handgun."
"Those two things don't mix," the sheriff added.
4. Students Predicted He Could Go on Shooting Spree
While parents and students at Marjory Stoneman Douglas High School are shocked and reeling at the massacre, the identity of the mass shooter is not surprising, according to a number of his former classmates.
Dakota Mutchler, a 17-year-old junior at the school, who for a time had been friends with the suspect, said that beside his talk about guns, Cruz also boasted about killing animals on social media.
"Everyone in the school that knew him speculated about him," Mutchler said, according to The Guardian. "When someone's expelled, you don't really expect them to come back. ... If they're expelled, they're gone. But of course, he came back."
Mutchler revealed the he cut off contact with Cruz after "he started going after one of my friends and threatening her."
Seventeen-year-old junior Victoria Olera had a similar account. "At first, he was really nice," she said, but later "he just changed. As far as I knew, he was like a future school shooter."
A third student who chose to remain anonymous added: "A lot of people were saying that it was going to be him. All the kids joked ... saying he was the one that screwed up at school, but it turns out everyone predicted it. That's crazy."
John Crescitelli, the parent of a student named Daniel, quoted what his son said about the killer: "If you were to pick one person you might predict in the future would shoot up a school or do this, it would be this kid."
5. Cruz's Adoptive Mother Died Last Year
Cruz lost his adoptive mother, Lynda Cruz, to illness in November, after she lost her battle against the flu and pneumonia.
Kathie Blaine, her cousin, told CNN that the teenager's father had died more than a decade ago due to a heart-attack.
Jim Lewis, a Ft. Lauderdale attorney who represents the family, explained that following the death of his mother, Cruz had been living with a friend's family who took him in.
"They offered him a home and tried to help the kid out because he really didn't have any other place to stay." Lewis said.
The family that Cruz was staying with are fully cooperating with the investigation and have allowed authorities access to search their residence, Lewis told CNN affiliate WPTV.
"They are heartbroken. The kid that lives here goes to that school and knows many of these kids. He is just as heartbroken and shocked as everyone else. They cared for this kid and really wanted to help him," the attorney explained.