The shooter who killed two Catholic school students and wounded more than a dozen others during Mass at a Minneapolis church once attended the same school and was reportedly “obsessed” with the idea of killing children, authorities said Thursday.

Identified as 23-year-old Robin Westman, he fired 116 rounds from a rifle through stained-glass windows while students celebrated the first week of classes at Annunciation Catholic School, Minneapolis Police Chief Brian O’Hara said.

“It is very clear that this shooter had the intention to terrorize those innocent children,” O’Hara said.

Acting U.S. Attorney Joe Thompson said videos and writings left by Westman revealed a disturbing hatred for nearly every group imaginable.

“The only group he did not hate was mass murderers,” Thompson said. “In short, the shooter appeared to hate all of us.”