Still, Bond said, there is no way for students and teachers to protect themselves when someone begins shooting with a weapon. He said even a security guard and locked doors could not have stopped the killer.

Without knowing the school’s security system, Kenneth Trump, president of consulting firm National School Safety and Security Services, stresses that schools need to be “looking for these lone wolf actors.”

“As a father, I would love to have a 100 percent guarantee that nothing bad will ever happen in my kids’ school, but as a rational school safety professional I know nobody can give me a 100 percent guarantee on safety,” said Trump.

But he has seen the danger drop at schools in the wake of Columbine. Dozens of shootings have been thwarted by students, teachers and principals sharing information and warning about students with weapons or plans to kill.