The former student who allegedly gunned down 17 people at a Florida high school spared the life of one, a student has claimed.

Fifteen-year-old Chris McKenna told a local paper that he came across suspected gunman Nikolas Cruz in the hallway just minutes before he allegedly started his rampage.

“You’d better get out of here,” Mr Cruz said, according to Chris. “Things are gonna start getting messy.”

Chris froze for a minute, he told the Sun-Sentinel, and then ran. He ran out of the building and into Aaron Feis, the assistant football coach, who was unlocking the school gates for dismissal.

“I told him I saw a gun,” Chris said. “He said ‘let me go check it out.’ Then he drove me to the baseball field, dropped me off, and went back to the school. That’s the last I saw of him.”

Florida shooting – in pictures Show all 10 1 /10 Florida shooting – in pictures Florida shooting – in pictures Police arrest a suspect in connection with the shooting at the Marjory Stoneman Douglas High School in Parkland, Florida Reuters Florida shooting – in pictures Parents wait for news after reports of a shooting at Marjory Stoneman Douglas High School in Parkland, Florida AP Florida shooting – in pictures Anxious family members wait for news of students AP Photo/Wilfredo Lee Florida shooting – in pictures Students being evacuated from the school AP Florida shooting – in pictures Students being evacuated from the school Getty Florida shooting – in pictures People gather waiting for word from students AP Florida shooting – in pictures Parents waiting for news on their children AP Florida shooting – in pictures People gather at a hotel where students were taken after the shooting Getty Florida shooting – in pictures Florida Governor Rick Scott speaks to the media as he visits Marjory Stoneman Douglas High School following the shooting AFP/Getty Florida shooting – in pictures Dr. Igor Nichiporenko, Medical Director Trauma, left, and Dr. Evan Boyer, Medical Director, Emergency Services, speak about treating victims and the suspect at a press conference outside Broward Health North hospital AP

Mr Feis was one of three staff members who were killed in the shooting. Witnesses said he threw himself in front of students to protect them when the gunfire started. He died in the hospital after being rushed into surgery for a gunshot wound.

Chris told the Sun-Sentinel that three of his classmates had been killed in the shooting, and a fourth injured.

“I’m in shock,” he said. “That’s the only thing I can feel right now.”

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Mr Cruz has been charged with 17 counts of premeditated murder. He is being held without bail, and has yet to enter a plea. In his first court appearance on Thursday, his court-appointed lawyer defended him a s a “broken human being”.

The student was previously expelled from Marjory Stoneman Douglas for “behavioural reasons,” according to Broward County Sheriff Scott Israel. Teachers told the Miami Herald they had been instructed not to let him on campus, for fear he could pose a safety threat.

Officials said they were still investigating Mr Cruz’s social media activity, including a YouTube comment apparently left by the teeanger, reading: “I want to be a professional school shooter.”

“We are looking into his social media posts, his movements, his conversations leading up to the shooting, as well as any other indicators that may be out there,” FBI special agent in charge Rob Lasky told reporters.

The shooting left at least 14 students and three staff members dead, and 14 wounded. The youngest of the victims was just 14.