At least 17 people were killed Wednesday in a high school shooting in Parkland, Florida, the Broward County Sheriff’s office said.

Authorities say they have taken 19-year-old former student Nikolas Cruz into custody in connection with the deadly shooting at Marjory Stoneman Douglas High School on Wednesday.

The school shooting suspect was arrested “without incident” an hour after allegedly leaving the Marjory Stoneman Douglas High School grounds.

Seventeen people were killed and more than 14 were injured in the Parkland, Florida school shooting.

Authorities believe the suspected shooter worked alone. More than 3,200 students attend ninth through 12th grade at the high school, which is staffed by approximately 130 teachers.

Broward County Sheriff Scott Israel confirmed in a evening news conference that Cruz is a former student of the high school who was expelled for disciplinary reasons, Fox News reports. Sen. Bill Nelson also told FOX that Cruz was wearing a gas mask during the shooting and may have been carrying smoke bombs.

In an interview Wednesday evening with CNN, Marjory Stoneman Douglas math teacher Jim Gard, who had Cruz as a student in 2016, was surprised to hear the news of his arrest. “He was a quiet kid in class, I never had any problems with Nick,” Gard said.

“Some of the girls in my class said that I guess he had some problems with some other girls, but that’s hearsay, and all that,” he added. “As far as my class goes, I remember an email or two from admin [expressing concern] but I can’t remember exactly what it said.”

However, Gard expanded on his account to the Miami Herald, telling the paper that he believed an email from the school administration circulated warning teachers that Cruz had made threats against other students. “We were told last year that he wasn’t allowed on campus with a backpack on him,” Gard said. “There were problems with him last year threatening students, and I guess he was asked to leave campus.”

Superintendent Robert Runcie of the Broward County School District told reporters outside the school they had received no concerns about Cruz. “We received no warnings,” he said. “Potentially there could have been signs out there. But we didn’t have any warning or phone calls or threats that were made.”

A student named Nicholas Coke interviewed on the scene by WSVN-7 described Cruz as a “loner.” Coke also recalled a time in middle school when Cruz kicked out a glass window before getting caught, according to the Miami Herald.

“He had a lot of problems in middle school,” Coke said.

“He’s been a troubled kid,” an unidentified student who said he knew Cruz told local media. “And he’s always had a certain amount of issues going on. He shot guns because he felt it gave him, I guess, an exhilarating feeling.”

“He always had guns on him,” another unidentified student told WFOR-TV, who said Cruz was never shy about showing off his guns. “The crazy stuff that he did was not right for school, and he got kicked out of school multiple times for that kind of stuff.”

Another unidentified student described the suspect to CBS News. “The kid was crazy,” the student said. “I had engineering with him a couple years ago and he wasn’t allowed to come to school with a backpack and he would threaten students and break glass and get into fights so he got kicked out of school.”

“All he would talk about is guns, knives and hunting,” former classmate Joshua Charo, 16, told the Miami Herald. “I can’t say I was shocked. From past experiences, he seemed like the kind of kid who would do something like this.”

Helen Pasciolla, a retired neighbor who lives in the Cruz family’s former neighborhood in Parkland, told the New York Times that Cruz and his brother, Zachary, who are both adopted, had regular behavioral problems.

Authorities have begun looking into Cruz’s social media profile, findings which Broward Sheriff Scott Israel described to reporters as “very, very disturbing.”

Unverified images on social media accounts cited by multiple media sources appear to show a man holding firearms, wielding knives like a claw, and a collection of guns on a bed.