The schoolhouse murder of 28 people in Connecticut in 2012 was impossible for me to grasp. Twenty were children. I could only document the tragedy through one family's grief. At the time, we didn't know the names or what terrible news they've just heard. Now, we know they are Gracie McDonnell's parents. She was in second grade. Through tweets and images, I've documented her parent's struggle to bear the unbearable.