Key facts related to the Connecticut elementary school shooting:
THE INVESTIGATION: Twenty-year-old Adam Lanza, was carrying an arsenal of hundreds of rounds of deadly ammunition -- enough to kill nearly every student in the school if given enough time, authorities said, raising the specter the bloodbath could have been far worse. Lanza shot himself in the head when he heard police approaching the classroom where he was gunning down helpless children.
He had multiple, high-capacity clips each capable of holding 30 bullets, and the chief medical examiner said the ammunition was the type designed to break up inside a victim's body and inflict the maximum amount of damage, tearing apart bone and tissue.
The gunman shot his mother four times in the head before going to the school and gunning down 26 victims there.
THE VICTIMS: All the victims at the school were shot multiple times with a high-power rifle, some of them up close. All six adults were women. Of the 20 children, eight were boys and 12 were girls. All the children were 6 or 7 years old.
Among the dead were popular principal Dawn Hochsprung and school psychologist Mary Sherlach, who rushed toward Lanza in an attempt to stop him and paid with their lives; Victoria Soto, a 27-year-old teacher who died while trying to hide her pupils; 30-year-old Lauren Rousseau, a teacher thrilled to have been hired this year, and Ana Marquez-Greene, a 6-year-old girl who had just moved to Newtown from Canada.
THE GUNMAN: Lanza was described as a bright but painfully awkward student who seemed to have no close friends. In high school, he was active in the technology club. The club adviser remembered that he had "some disabilities" and seemed not to feel pain like the other students. That meant Lanza required special supervision when using soldering tools, for instance. He also had an occasional "episode" in which he seemed to withdraw completely from his surroundings, the adviser said.
Authorities said Lanza had no criminal history, and it was unclear whether he had a job.
THE SCENE: Families sought to comfort each other during Sunday church services and vigils devoted to impossible questions like that of a 6-year-old girl who asked her mother: "The little children, are they with the angels?"
Many of Newtown's 27,000 people wondered whether life could ever return to normal, and, as the workweek was set to begin, parents pondered whether to send their children back to school. Signs around town read, "Hug a teacher today," "Please pray for Newtown" and "Love will get us through."
THE PARENTS: One of the parents who lost a child in the attack spoke publicly about his loss.
Robbie Parker fought back tears and struggled to catch his breath as he described his 6-year-old daughter, Emilie, as a little girl who loved to draw. He also reserved surprisingly kind words for the gunman, saying he was not mad and offering sympathy for the gunman's family.
To the man's family, he said, "I can't imagine how hard this experience must be for you."
THE GUNS: Federal authorities visited local gun ranges but found no evidence that the gunman trained for the attack or was an active member of the recreational gun community.
Investigators also have interviewed gun dealers trying to determine whether there was any training or other behavior that precipitated the attack.
THE HISTORY: The Newtown massacre is the second-deadliest school shooting in U.S. history and one of the deadliest mass shootings around the world. A gunman at Virginia Tech University killed 33, including himself, in 2007. Only Virginia Tech and the mass killings of 77 in Norway last year had greater death tolls across the world over the past 20 years.