Ten years ago, on April 20, 1999, the nation – and the world – looked on in shock as two 17-year-olds, Eric Harris and Dylan Klebold, went on a vicious gun rampage at Columbine High School in Colorado, killing fellow 12 students and a teacher.

Unlike most massacres, it was not the work of a lone gunman but the combination of two warped minds that had become engrossed by violence and revenge.

What are your memories and thoughts about that terrible day? Have the authorities learned the right lessons in identifying such people before they act? Have schools learned to prevent the bullying and ostracism believed to have played a part? Do the police know better how to react to such events? What can we as a society do to prevent the development of such similar evils?

We'd like to know your thoughts and stories. The best of them will be published on msnbc.com.

Thank you.