The shooter who killed two Catholic school students and wounded more than a dozen youngsters once attended the same educational institution and was “obsessed” with the idea of killing children, authorities said on Thursday.The shooter, 23, fired 116 rifle rounds through stained-glass windows while the youngsters sat in pews at Mass at the 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 added.Acting US Attorney Joe Thompson said videos and writings the perpetrator posted showed that he “expressed hate towards almost every group imaginable.”Two children, aged 8 and 10, died in the shooting.City officials on Thursday increased to 15 the number of wounded children, all aged between 6 and 15, in addition to three parishioners in their 80s. Most of those wounded were expected to survive, O’Hara said.What is the FBI saying about the shooting?Meanwhile, more details emerged on Thursday regarding what unfolded just before 8:30 a.m. local time (1330 GMT) on Wednesday morning.For instance, one boy acted as a human shield to protect a schoolmate as the horrific scenes unfolded, county health officials said.“There’s a lot of maybe unrecognized heroes in this event, along with the children that were protecting other children,” said Martin Scheerer, a director at Hennepin Emergency Medical Services. “The teachers were getting shot at. They were protecting the kids.”FBI Director Kash Patel said there was evidence the incident was an “act of domestic terrorism motivated by a hate-filled ideology.”The shooter’s writings included anti-Catholic rhetoric and a call for the assassination of US President Donald Trump, Patel said.‘This is about guns,’ says Minneapolis mayorMinneapolis Mayor Jacob Frey, a Democrat, was joined by gun-control advocacy groups, calling for a ban on certain high-capacity semi-automatic rifles.The mayor took issue with those who say gun violence is a mental health issue, not connected to the accessibility of firearms.“People who say, ‘This is not about guns,’ you gotta be kidding me: this is about guns,” Frey told ABC News on Thursday.“A 10-year-old boy had more courage hiding in a church pew while his friend shielded him with his body than I have seen from far too many lawmakers more beholden to a gun lobby than a child,” said Angela Ferrell-Zabala, executive director of Moms Demand Action, a gun violence prevention group.