2:18 PM PT -- The Atlanta division of the FBI confirmed the agency investigated threats made by then-13-year-old suspect Colt Gray via Discord in May 2023. The threats ... which included pictures of guns ... were to commit a future school shooting -- but no mention of when or where.

The FBI referred the threats to the Jackson County Sheriff's Office ... and deputies visited the home to interview the suspect and his father. The suspect denied making the threats ... and although there were guns in the home ... the father told deputies Colt did not have "unsupervised access."

It was determined there was no probable cause for arrest or any other action.

The suspect charged with murdering four people at a Georgia high school this week was banned from Discord for violating their extremism policy.

A rep for the popular messaging platform tells TMZ ... an account believed to be connected with Colt Gray was created in early April 2023 and banned just six weeks later for violating the platform's anti-extremism policy.

We're told "Discord’s Safety team immediately responded to law enforcement," provided all necessary info for their investigation, and removed the user from the platform.

That said, Discord's spokesperson says their subsequent investigation has not revealed any evidence Gray used the platform to plan yesterday's attack.

Discord's violent extremism rules say the service does not allow any promotion or organization of violent actions ... banning both members of violent extremist groups and individuals not associated with these groups from advocating for these beliefs.

Gray was arrested Wednesday morning at Apalachee High School in Winder, GA ... with cops saying he surrendered as soon as they arrived on the scene.

Colt's accused of killing 14-year-old students Mason Schermerhorn and Christian Angulo, teachers Christina Irimie and Richard Aspinwall, and injuring nine other people. He's been charged with four felony counts of murder and reportedly will be prosecuted as an adult.