After Adam Lanza opened fire at Sandy Hook Elementary School in Newtown, Conn. Friday morning, police continue to search for motive as more details of the tragedy emerge.Associated Press that investigators had found "very good evidence ... that our investigators will be able to use in painting the complete picture, the how and, more importantly, the why."According to CNN, on the Tuesday before the shooting, Lanza had unsuccessfully attempted to purchase a gun in the nearby town of Danbury. Three days later on Friday morning, Lanza killed his mother at their home before driving her car over to the elementary school. He took with him three guns, a semiautomatic .223-caliber Bushmaster rifle and two pistols, all of which belonged to his mother.He then forced his way inside and opened fire in two classrooms. Police received the first report of the shooting around 9:30 a.m. The assault lasted approximately 20 minutes before Lanza took his own life. All schools in the area were placed on lockdown after the shooting, as parents rushed to the school for news about their children.The attack resulted in the death of 28 victims, which includes 20 children and six adults who were killed at the school, the shooter, and his mother.