From Columbine to Sandy Hook, Peter Langman, a practicing psychologist in Allentown, has been looking inside the minds of school shooters. His book Why Kids Kill: Inside the Minds of School Shooters, and his website, schoolshooters.info, share what he has learned from studying those responsible.

Langman was as naive as the rest of the public when in 1999, the shootings at Columbine took place. In the preface of his book, he began, "I did not want to write this book. I deliberately resisted the thought that this book needed to be written. I wanted to believe that the rash of school shootings in the late 1990s was over. It was a naive hope."

But just 10 days after the attack at Columbine, a teenager was admitted to the psychiatric hospital where Langman worked due to concerns that he might "go Columbine."

"He had a hit list on his website and had engaged in other disturbing and threatening behaviors," he wrote. Since then, Langman has evaluated one or two potential school shooters a year.

Langman places the minds of school shooters in three categories: psychopathic shooters, psychotic shooters, or traumatized shooters. Asked to explain what that means to the ordinary person, he said, "People leak their violent intentions."

"If people make direct threats, which they often do, those need to be responded to," he explained. "Many times shooters told people exactly what they are going to do. They announced that they are going to come with a gun and kill. Often people brush it off.

"Often there are direct threats," he continued. "Sometimes, it is one kid trying to talk another kid into joining him. Sometimes kids warn their friends to stay away. 'Hey I'm going to do something big in the school on Monday don't be there.' That is an obvious warning sign.

"Sometimes they brag about what they are going to do. Sometimes they post messages, photos or videos of themselves posing with weapons on Facebook or their own website."

Langman believes that the signs are often there but are not believed, or no one takes action.

"Whether they are teachers, parents or other kids, they should all be educated as to what they should look for and what to do when they see it. If kids see these things, they need to report it to people at the school."

One thing that Langman observed was that in many cases, the shooter did not purchase the weapons.

"Often, there are guns in the house. The parents think that the guns are secured, but they are not. That's another thing to keep in mind. If you have guns in the home, they better really be secured, and I am not really sure that they can be secured if you have a teenager who was determined to get them," said Langman.

"If your teenager is struggling with anger, depression, violent thoughts, is obsessed with violence, or obsessed with what happened at Columbine and Virginia Tech, you should get the guns out of the house."

In many attacks, the kids took the weapons from parents, grandparents or neighbors. Langman suggests that if you own a gun and there is any chance that a youth might be visiting, could steal a key, or drill through a lock, the best thing would be to store your gun at a gun club.

Asked what you should tell your child about what happened in Sandy Hook, Langman replied, "If the kids are very young, 5 or 6 years old like some of the victims were, if they are not aware of what happened, I don't think there's any need to frighten them by telling them that this is what happened.

"If they hear about it, or see something on television, and they have questions, then it makes sense to talk in an age-appropriate way about what happened. You can reassure them that one bad man did it, and he is not around anymore, so he can't hurt anybody," he added.

"The best thing to do in terms of prevention is educating parents and teachers and students about what constitutes a warning sign of violence," Langman advised. "That is more important than putting in more metal detectors or additional security guards. I think that it is best to catch it before it happens."

For additional information, see: schoolshooters.info.