The 15-year-old shooter who allegedly opened fire on his Michigan High School on Tuesday (local time) posted a chilling countdown on Instagram just hours before the bloodshed.
Ethan Crumbley has been charged with murder and terrorism after killing four fellow students and injuring seven others at Oxford High School.
Teen showed 'concerning behaviour'
Authorities have revealed a series of shocking details about the “senseless” and “brutal” shooting, including that Crumbley was previously flagged for “concerning” behaviour in the classroom.
Sheriff Mike Bouchard told reporters that his parents had been summoned by the school on the day of the attack but the teenager remained in class.
It’s unclear what troubled school officials but investigators believe the gun was already at the school by that stage.
"There is nothing that he could have faced that would warrant senseless, absolutely brutal violence on other kids," the sheriff said.
Alleged shooter recorded frightening video
Police have also told a court hearing that Crumbley allegedly recorded a video the night before in which he discussed shooting and killing students.
Prosecutor Karen McDonald described Tuesday's shooting as "premeditated", based in part on a "mountain of digital evidence" collected by police but a motive is yet to be determined.
"This was not just an impulsive act," McDonald said.
Parents count face charges
The 9mm Sig Sauer gun Crumbley used to carry out the attack was bought by his father the week before, with charges now being considered against the parents.
"Owning a gun means securing it properly and locking it and keeping the ammunition separate,” MacDonald said.
Social media posts warn of shooting
Authorities have uncovered social media posts in the wake of the attack which detail unnerving threats of a shooting at the roughly 1700-student school.
The teen allegedly posted a countdown on Instagram, writing: "Now I become death — destroyer of worlds — see you tomorrow Oxford."
Crumbley had also reportedly posted photos of the gun, and him firing it, in the lead-up to the school shooting.
Seven students remain in hospital
Officers stormed the school about lunchtime on Tuesday (local time) and arrested Crumbley in a hallway within minutes of the shooting.
Crumbley has been arraigned on charges of murder, attempted murder, terrorism causing death and gun crimes. He is charged as an adult.
The four students who were killed were identified as 16-year-old Tate Myre, 14-year-old Hana St Juliana, 17-year-old Madisyn Baldwin and 17-year-old Justin Shilling.
A teacher who received a graze wound to the shoulder left hospital, but seven students ranging in age from 14 to 17 remained in hospital overnight with gunshot wounds.
Do you have a story tip? Email: email@example.com.