The anonymous tips were sent to the F.B.I. last May from as far away as Australia, warning that a user on Discord, a social media platform, had threatened in a chat group to possibly “shoot up a middle school.” The authorities were led to a 13-year-old living in Jackson County, Ga.

A report from the Jackson County sheriff’s office, obtained by The New York Times, detailed how investigators looked into but were unable to definitively link those threats to the teen, who is now in custody after a shooting on Wednesday morning at his high school in Winder, Ga. He is accused of killing two students and two teachers.

Hours after the shooting, the F.B.I. disclosed that law enforcement had investigated the online threat, which was made in May 2023. But the report from the sheriff’s office reveals more about how the authorities were able to trace the post to the teenager, and why — after interviewing the boy and his father — they did not take further action, other than a warning to his middle school.

According to the report, the F.B.I. received several tips from users with internet addresses in Palmdale, Calif., Los Angeles and Cockburn, a city in Western Australia, which included the posts made in a group chat on Discord. The email associated with the account belonged to Colt Gray, the teen accused of the shooting at his school.

The investigators found that the username on the Discord account had been written in Russian. “Translation of the Russian letters spells out the name Lanza,” the investigator wrote in his report, noting that it was the surname of the perpetrator of the 2012 massacre at Sandy Hook Elementary School in Newtown, Conn., in which 20 students and six teachers were killed.

In interviews with investigators, both Mr. Gray and his father, Colin Gray, said that they did not speak Russian, and the boy denied that he had been the author of the threats. He said that he had previously had a Discord account, but had deleted it, claiming he had been repeatedly hacked and was “afraid someone would use his information for nefarious purposes,” an investigator wrote.