Fifteen years ago today, I left Philadelphia to cover the Oklahoma City bombing. Investigators check the damage to the Murrah Federal Building one day later, in the top photo, and 10,000 residents gather for a memorial service several days later, seen in the bottom photo.

Many journalists found this to be one of the most emotionally difficult assignments of our time, but the effects on the Oklahoma City community are still being measured, and the attack foreshadowed more national crises in the years that have followed.

To learn more about journalism and psychologocal trauma, please visit http://dartcenter.org/