Law enforcement officials seeking a motive for a shooting at Nashville’s Antioch High School on Wednesday morning are examining alarming social media posts and writings tied to a teenager police say shot and killed a 16-year-old girl.

A teenager who opened fire with a 9 mm pistol in his Nashville high school cafeteria fired a total of 10 shots within 17 seconds of entering the room, according to police.

An AI gun detection system installed in a Nashville, Tennessee high school couldn’t spot the gun a 17-year-old used to fatally shoot another student and himself earlier this week, according to district officials.