The 9mm Sig Sauer used to kill 3 people and wound eight others at a Michigan high was bought by the 15-year-old suspect's dad on Nov. 26, authorities say.
Oakland County Sheriff Michael Bouchard said late Tuesday that the suspect had practiced shooting with the gun and posted pictures of it and the target. Bouchard said he did not know why the boy's father bought the gun.
Bouchard said several students from the shooting remain in critical condition, including 14-year-old on ventilator.
Authorities have said they are still trying to determine a motive for the shooting at Oxford High School in Oxford Township.
THIS IS A BREAKING NEWS UPDATE. AP's earlier story follows below.
A 15-year-old sophomore opened fire at his Michigan high school on Tuesday, killing three students and wounding eight other people, including one teacher, authorities said.
Oakland County Undersheriff Mike McCabe said at a news conference that investigators were still trying to determine a motive for the shooting at Oxford High School in Oxford Township, a community of about 22,000 people roughly 30 miles (48 kilometers) north of Detroit.
McCabe said he was aware of allegations circulating on social media that there had been threats of a shooting at the roughly 1,700-student school before Tuesday's attack, but he cautioned against believing that narrative until investigators can look into it.