What's Causing School Shootings?

There have been (so far, as this is written) 25 school shootings since that which occurred at Columbine High School in Colorado. I remember that day dimly, as I was in shock, along with almost everybody closeby. and I was. I was a security guard at another school that day, and I wondered how long it would be before such violence came to my school. As an UNARMED security guard, what could I do to stop it from happening? They need to stop looking at the guns when this happens, and start trying to find the underlying reasons, such as the mental instability of some students who have mental problems, and are known to have them. Somebody needs to look elsewhere than at the guns, and how such shooters get them. They need to start looking at what's in the MINDS of potential shooters, and paying attention to that, so as to stop such shootings from happening at all. (Just common sense)