The FBI was warned about the teenager who allegedly carried out a mass shooting at his former school in Florida, the BBC understands.
Nikolas Cruz, who has been charged with 17 counts of premeditated murder, reportedly left a comment on a YouTube video last year stating: "I'm going to be a professional school shooter."
A user alerted authorities to the post.
Teachers were also warned about Mr Cruz, who was not allowed on campus with a backpack, US media report.