NOTE: This post will be continually updated as new information comes in. Video and photos are below. All times Eastern.
UPDATE 6:30 p.m.: Originally it was thought that Adam Lanza, the gunman, shot his mother at the Sandy Hook Elementary school, where she was a teacher's aide. ABC has learned that, in fact, Nancy Lanza was killed at her home (by her son) prior to the massacre. He then drove to the school, where he killed 20 children and six adults, before killing himself.