The man accused of opening fire at a Florida high school on Wednesday, killing 17 people, was a troubled former student who loved guns and was expelled for unspecified disciplinary reasons, police and former classmates said.

Nikolas Cruz, 19, was arrested about an hour after a shooting rampage at Marjory Stoneman Douglas High School in Parkland, Florida, Broward County Sheriff Scott Israel told reporters.

Cruz, who had been expelled from the school for reasons that have not been made public, was found with multiple ammunition magazines and one AR-15-style rifle, Israel said.

"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," Israel said.

Chad Williams, 18, a senior at Stoneman Douglas High school, remembered Cruz as a troubled classmate from middle school. He said Cruz would set off the fire alarm, day after day, and finally got expelled in the eighth grade.

More recently, Williams saw Cruz carrying several publications about guns when they ran into each other at the high school. Williams thought Cruz was there to pick up a younger sibling.

"He was crazy about guns," Williams told Reuters by the side of the road near the high school. "He was kind of an outcast. He didn't have many friends. He would do anything crazy for a laugh, but he was trouble."

Jillian Davis, 19, said she was in a school Junior Reserve Officer Training Corps with Cruz in the 9th grade. She remembered him as a quiet and shy young man who would almost change personality when angry. He talked a lot about guns and knives but no one took him seriously, she told Reuters.

"I would say he was not the most normal or sane kid in JROTC. He definitely had a little something off about him. He was a little extra quirky," said Davis, who graduated from the school last year.

'A LITTLE OFF'

Math teacher Jim Gard told the Miami Herald Cruz had been banned from returning to campus while carrying a backpack.

"There were problems with him last year threatening students, and I guess he was asked to leave campus," Gard told the newspaper in an interview.

Administrators sent an email to teachers warning them about Cruz, Gard told the paper.

Another student, 17-year-old junior Dakota Mutchler, told reporters at a hotel in nearby Coral Springs that he hadn't spoken with Cruz in more than a year. Students were reuniting with their parents and friends at the hotel.

Mutchler said he declined to communicate with Cruz, a former friend, after the suspect contacted him two weeks ago on Snapchat.

"Everybody that knew of him had a sort of suspicion about him," Mutchler said. Cruz had once told him he had used a pellet gun in his backyard for target practice, he said.

Travis Julmice, an 18-year-old senior, said he had not been in a class with Cruz since middle school.

"You could tell he was a little off," Julmice told Reuters at the Coral Springs hotel. "He was always like a troubled kid, getting in-school suspension a lot. And detentions."

However, Broward County Public Schools Superintendent Robert Runcie told reporters outside the school after the shooting that the school had no indication Cruz was a danger.

"Typically, you see in these situations that there potentially could have been signs out there," he said. "But we didn't have any warnings, there weren't any phone calls or threats that we know of that were made."

Runcie later said Cruz was still a student at Broward County Public Schools but declined to provide further details.

Israel said earlier Cruz may have been enrolled at Taravella High School in Coral Springs after his expulsion but the sheriff did not know if Cruz still attended Taravella.