The 19-year-old who confessed to the shooting at Marjory Stoneman Douglas High School in Parkland, Florida, may have been on authorities' radar as far back as 2016.
Outlets report the suspect was investigated by state officials after he posted a video on Snapchat showing him cutting both of his arms. He also reportedly said he planned to buy a gun.
Officials interviewed the suspect but ultimately decided he was stable and already receiving adequate support from a counselor.
The news comes a day after the FBI admitted it failed to investigate a tip it received about the suspect in January.
Additional reporting from Newsy affiliate CNN.