The 15-year-old Michigan high-school student accused of gunning down his classmates Tuesday used a gun that was purchased by his father on Black Friday, according to the Oakland County Sheriff’s Office. “The person that’s got the most insight of the motive is not talking,” Sheriff Michael Bouchard told reporters late Tuesday, hours after the attack at Oxford High School that left three students dead and eight others wounded. The teen suspect has not been identified, but Bouchard revealed that he allegedly used a 9mm Sig Sauer handgun belonging to his father. The gun was purchased on Friday, just days before the massacre, and the suspect is said to have posted photos with the weapon on social media.

Investigators say they believe he was preparing to gun down more students just before he was stopped by police, according to Bouchard. When sheriff’s deputies confronted him and “they took [the gun] from him, he had a loaded firearm and he was coming down the hall,” Bouchard said, noting that the gun had seven rounds. “That, again, I believe interrupted what potentially could have been seven more victims.”