More than a year before the deadly shooting at Apalachee High School in Winder, Ga., the sheriff in a neighboring county was told by the F.B.I. of school shooting threats that a local student was believed to have posted on the internet chat site Discord.

An investigator interviewed the student, who was 13, for less than 10 minutes, and came away saying he could not determine whether the teen had made the threats. He closed the case, and his supervisor said the teenager would be monitored.

Now that same teenager is accused of carrying out the rampage that killed two students and two teachers last week at Apalachee, and his earlier encounter with the police has raised questions about whether more aggressive intervention then could have prevented the deadly shooting.

Cybersecurity experts and law enforcement officers who specialize in tracking online activity say that the investigator, from the Jackson County Sheriff’s office, gave up too quickly and that the handling of the case underscores a lack of training and expertise among rank-and-file officers in the nation's 18,000 police agencies. Those officers are often the first line of investigation into online threats of violence, working in an ever-shifting universe of apps and chat rooms.

Seeking information from social media platforms has become routine for many police agencies, who use it to piece together timelines and behavioral profiles. Instagram, YouTube and TikTok have entire divisions dedicated to responding to law enforcement inquiries and complying with subpoenas that officers have obtained for user account information. But the investigator in Jackson did not seek such information.

“If I had subpoena power, which law enforcement officers do, with a very high degree of confidence I would be able to identify who the author of those threats was,” said Paul Raffile, a cyber-intelligence analyst who has collaborated with law enforcement agencies on investigating sexual extortion cases and other internet scams.