My brother would like to know why where kids crying today during a school seminar on in school shootings.?

Ok i told him beacause school shootings can often bring to families every parents worst nightmare and can oten times be prevented and he also wanted to know why was columbine one of the most highly publicized school shootings in american history and the oes that have happend afterwords werent as highly talked about.Can someone plz help me come up with an answer to this.