"I was standing in front of the teacher when she was shot," a shaken seventh grader tells the BBC, near the gates of Debsirin School in Nonthaburi. One 18-year-old student told Reuters he initially thought firecrackers were going off. One grieving teacher told the BBC his friend was among the dead. In February, a head teacher and a female student were shot by an 18-year-old gunman during a school siege in southern Thailand. "This shouldn't have happened," the boyfriend of one of the killed teachers told reporters, clearly distressed and trying to hold back tears.