The Federal Bureau of Investigation was warned last year about an ominous online comment by the 19-year-old man accused of killing 17 people at his former high school but was unable to locate him, an agent said on Thursday.
Authorities said the ex-student, identified as Nikolas Cruz, walked into the Marjory Stoneman Douglas High School in Parkland, near Miami, on Wednesday and opened fire with an AR-15-style assault rifle in the second-deadliest shooting at a public school in U.S. history.
Cruz may have left warning signs on social media in the form of a comment on a YouTube video that read "I'm going to be a professional school shooter."