MIAMI — The campus monitor who first spotted Nikolas Cruz just before the mass shooting at a Florida high school told investigators he initially tried to follow the teen but wasn't able to catch up with him.

"He's beelining," Andrew Medina told Broward County detectives in an interview. "He's got his head down. He's on a mission, you know. He's on a mission."

The State Attorney's Office released video and a transcript Tuesday of the 25-minute interview. Medina, a baseball coach and unarmed campus monitor, told detectives he watched Cruz get out of an Uber the afternoon of Feb. 14 and head straight to the building where 17 people would be killed minutes later at Marjory Stoneman Douglas High School.

Medina, 39, had been riding a golf cart around campus, unlocking gates, about 20 minutes before dismissal. Medina radioed the campus monitor of the building where Cruz was heading, warning of a suspicious person. Medina said he recognized the 19-year-old as a problem student who was no longer enrolled at the school.

"I'm telling you, I knew who the kid was," Medina said. "Because we had a meeting about him last year, and we said, 'If there's gonna be anybody who's gonna come to this school and shoot this school up, it's gonna be that kid.'"

Medina said he tried to follow Cruz, not realizing the teen might be armed.

"He sees my golf cart and he runs," Medina said. "He starts running to the building, inside the building."

Medina said he began hearing shots from insides less than a minute later.

"I'm getting out," Medina said. "And then I hear, pop, pop, pop, pop, pop, pop."

Medina said he didn't immediately report an emergency code because he hadn't seen a gun and didn't want to needlessly bring a SWAT response. Instead, Medina picked up the armed school resource officer, Scot Peterson, in his golf cart and drove back over to the building. Once there, the deputy told Medina to leave, so Medina said he headed back to the front of the school.

Peterson has been widely criticized for his lack of action. He resigned and retired from the Broward Sheriff's Office eight days after the shooting when video surveillance footage showed him standing outside the building during the rampage.

Cruz has been charged with 17 counts of first-degree murder in the attack. Lawyers have said he would plead guilty in exchange for a life prison sentence, but prosecutors are pursuing the death penalty.