PARKLAND, Fla. – An unarmed campus monitor spotted Nikolas Cruz at Marjory Stoneman Douglas High School just before the shooting and warned staff, according to newly released court documents.

School resource Deputy Scot Peterson resigned after reports that he failed to engage Cruz during the shooting. Peterson has said that he didn't engage because he was unsure from where the gunfire was coming. However, the monitor's interview with Broward County sheriff's deputies appears to contradict these statements.

Andrew Medina, who provides unarmed security in front of the school, told deputies on the day of the shooting that left 17 people dead he noticed an Uber pull up to the school and drop off a young man with a black bag.

Medina, who is also the school's baseball coach, became suspicious because of the man's demeanor and thought he recognized him as a former, troubled student, according to a transcript of his interview.

"He's beelining. He's got his head down. He's on a mission, you know. He's on a mission," he said.

Medina said he followed in his golf cart and radioed another campus monitor. He said Cruz was headed for the 1200 building, where all the victims were killed.

"I quickly call my security guard guy who's in the 1200 Building and I said, um, (David) Taylor, Coach Taylor, got a suspicious subject on campus, Medina said in the transcript. "Got a black bag in his hands. Keep your eyes open because I think he's going into your building. So, you know, careful. You know, keep your eyes open."

But the warning wasn't enough. Taylor was unarmed and Nikolas Cruz was carrying an AR-15 semi-automatic rife.

"I'm talking about he ran in and not even a minute after he was in we heard -- I heard the first bang, like pow. And then I hear, pop, pop, pop, pop, pop, pop," he said.

After hearing gunfire, Medina said he immediately alerted Peterson.

"But once I heard the shots, I told the deputy, there's some crazy shots going on. Then when he heard the shots, that's when he was, like, we got a shooter on, on campus, you know."

Later in the interview, Medina said he had recognized the gunman as "Nik," a former student who had exhibited strange behavior and "always had problems."

"We always was watching him, you know. Like, it was one of those kids that we always kept an eye on," Medina said, explaining to authorities that Cruz always wore black and made racist comments.

He said he texted the other security guards Cruz's name during the shooting.

"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.