A year ago 20 innocent children and six adults in the Sandy Hook Elementary School in Newtown, Conn. were slaughtered by an armed, crazed gunman. It was a horrible event that shocked the nation and brought calls to do something about these events.

Unfortunately we seem to have done little. On Friday, another disturbed individual, a student who apparently had a grudge against a teacher, brought a gun to school to settle his score. He wound up wounding another student before shooting himself. His school is in Centennial, Colo., not far from Columbine High School, where 12 students and one teacher were killed in 1999, and not far from the Aurora., Colo. movie theater where 12 people were killed by a shooter last year.

What we have learned, in the years since Columbine, is how to train schools and police to react once the shooter has entered the school. But keeping the shooters from developing and carrying out their plans? We still have a long way to go.

We know there are usually warning signs well ahead of these incidents. Teachers and fellow students may hear talk of plans that sound too crazy to be taken seriously. Potential shooters may post dark and threatening messages on the internet for all to see.

We can all do more to end these kinds of events by listening, by taking these red flags seriously and by reporting them.

The best time to stop these attacks is before they happen.