The 19-year-old ex-student, who has been detained by Broward police, has not been publicly identified as a suspect. But a law-enforcement source identified him as Nicolas Cruz.

“We were told last year that he wasn’t allowed on campus with a backpack on him,” said math teacher Jim Gard, who said Cruz had been in his class last year. “There were problems with him last year threatening students, and I guess he was asked to leave campus.”