The 14-year-old student who killed four of his schoolmates in US's Georgia was questioned last year by police about online threats, the Federal Bureau of Investigation (FBI) said.
In May 2023, Colt Gray was questioned by police who believed he was behind internet posts that contained images of guns, warning of a school shooting.
The FBI said its National Threat Operations Center had alerted local law enforcement after receiving tips about "online threats to commit a school shooting at an unidentified location and time".
After the location of the threats were determined, the police interviewed the teen and his father.
While the teen denied sending the threats, his father told police that he had hunting guns in the house but the then 13-year-old "did not have unsupervised access to them".
"At the time, there was no probable cause for an arrest or to take any additional law enforcement action on the local, state or federal levels," the FBI said in a statement.
On Wednesday, the boy used an assault rifle to open fire in Apalachee High School, killing two teachers and two student, investigators say.
Eight other students and one teacher were injured in the attack. Gray was arrested from the school premises and will be tried as an adult.
The school sent out a message to parents saying it was "currently in a hard lockdown after reports of gunfire."
Survivors recounted the moment when Gray began attacking the students. One student told BBC that she saw him leave a class after a maths lesson and when he returned he had a gun in his hand. One of her classmates saw the gun and refused to open the door for Gray even as he continued to pound on it.
Gray then moved to the next classroom and opened fire.
According to the BBC, this was the 23rd US school shooting of 2024. So far 11 people have died and 38 have been injured in such attacks this year.
