The teenage gunman who killed a classmate at an Oregon high school on Tuesday was armed with a military-style rifle and a semi-automatic handgun that he obtained from his family’s home, and had no apparent link to his victim, police said on Wednesday.

Police said an autopsy of the suspect, Jared Michael Padgett, 15, confirmed that he died of a self-inflicted gunshot wound after exchanging fire with police inside Reynolds High School in the town of Troutdale, a Portland suburb.

Troutdale Police Chief Scott Anderson declined at a news conference to offer any explanation for what may have driven Padgett to walk into a boy’s locker room at the school and shoot a fellow freshman student, 14-year-old Emilio Hoffman.

“At this time it would be inappropriate to discuss a motive,” Anderson said, adding that the investigation was continuing.

But he credited a school gym teacher, Todd Rispler, with preventing further loss of life. Rispler was grazed by gunfire as he encountered Padgett but made his way to the school office to warn administrators of the attack and initiate a lockdown, Anderson said.

Anderson said Padgett opened fire with an AR-15-style rifle and also was carrying a semi-automatic pistol that he did not use, as well as a knife and nine loaded ammunition magazines capable of holding several hundred rounds.