Sue Klebold said this quote

There is perhaps no harder truth for a parent to bear, but it is one that no parent on earth knows better than I do, and it is this: love is not enough. My love for Dylan, though infinite, did not keep Dylan safe, nor did it save the 13 people killed at Columbine High School, or the many others injured and traumatized. I missed the subtle signs of psychological deterioration that, had I noticed, might have made a difference for Dylan and his victims - all the difference in the world.

~ Sue Klebold