This says something fundamental about these sorts of people who target children. Especially in religious schools, and here attending Mass in the morning.
There may be enough data points to strongly suspect what the "murder-suicide" pattern is driven by, although if you're willing to wade in this abyss, you'll also need to look at the other target patterns. Also keep in mind how "crazy" each set of murderers are, plus there's the Sudden Jihad Syndrome.
You might want to start with the Instawife, Helen Smith, who's a forensic psychologist. In 2020 in the wake of Columbine she wrote _The Scarred Heart: Understanding and Identifying Kids Who Kill_ it's said to be very good: https://www.amazon.com/dp/0615112234