According to Broward County mayor Beam Furr, who spoke to CNN's Anderson Cooper on Wednesday night after Governor Rick Scott's press conference, Cruz had been previously been a patient at a mental health clinic.
"(The kids at the school)... they thought if any student was going to do it, it'd be this student. So I don't know exactly if he was on law enforcement's radar, but it wasn't like there wasn't concern for him. He had not been back to the clinic for over a year. There's been a time where he was receiving treatment and then stopped."
Cruz, 19, was a former student at the high school, but had been expelled in Spring 2017.
Multiple students told news outlets that students and teachers had suspected Cruz as a potential threat.
"All he would talk about is guns, knives and hunting," Cruz's former classmate Joshua Charo 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."
"He used to tell me he would shoot rats with his BB gun and he wanted this kind of gun, and how he liked to always shoot for practice," Charo said.
"Honestly, a lot of people were saying that it was going to be him," a student told WSBTV. "A lot of kids threw around jokes like that, saying 'this is the one that's going to shoot up the school,' but it turns out everyone predicted it. That's crazy."
Jim Gard, a math teacher who had Cruz as a student last school year, told the Herald that Cruz was not allowed on campus following his expulsion.
"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."
Broward County Sheriff's Department reported at 3:22 p.m. that Cruz had been apprehended and arrested. A video was later released.
The victims were transported to Broward Health Medical Center and Broward Health North Hospital. Twelve of the 17 victims died inside the school, three outside the building and two after being transported to the hospital. Five of the injured remain in critical condition.