Last Updated 4:58 p.m. ET
The massacre of 26 children and adults at a Connecticut elementary school elicited horror and soul-searching around the world even as it raised more basic questions about why the gunman, a 20-year-old described as brilliant but remote, was driven to such a crime and how he chose his victims.
Investigators were trying to learn more about Adam Lanza and questioned his older brother, who was not believed to have been involved in the rampage at Sandy Hook Elementary.
Police shed no light on the motive for the second-deadliest school shooting in U.S. history.
A law enforcement source told CBS News that Adam Lanza had three weapons with him during the attack: Two handguns (a Sig Sauer and a Glock), and a Bushmaster .223 assault rifle; spent shells were found in the school. Those three weapons were registered to his mother.
There was also a fourth weapon (a long gun) found in the car he drove to the school.
In addition, the source told CBS News there were "a few" other weapons found at the mother's house. The registry of the weapon in the car and at the house are still be checked. The tracing of all the weapons - such as where and when they were purchased - is still being conducted.
The Associated Press reports a Henry repeating rifle, an Enfield rifle and a shotgun were recovered. It was not clear exactly where those weapons were found.
Lanza is believed to have suffered from a personality disorder and lived with his mother, said a law enforcement official who was briefed on the investigation.
Lanza's aunt said her nephew was raised by kind, nurturing parents who would not have hesitated to seek mental help for him if he needed it.
Marsha Lanza, of Crystal Lake, Ill., said she was close with Adam Lanza's mother, Nancy, and sent her a message on Facebook on Friday morning asking how she was doing. Nancy Lanza never responded.
Marsha Lanza described Nancy Lanza as a good mother and kind-hearted.
If her son had needed counseling, "Nancy wasn't one to deny reality," she told The Associated Press late Friday.
Marsha Lanza said her husband saw Adam as recently as June and recalled nothing out of the ordinary about him.
A nurse who had been with the school for 15 years, told CBS News' Scott Pelley that no one knows Nancy Lanza and that she was not a staff teacher, after earlier reports said Nancy Lanza worked at the school. The nurse said its conceivable that Nancy Lanza was a subsitute that she never met, but very unlikely. No other staff member the nurse has talked to has ever heard of Nancy Lanza. The nurse also knows of no connection between the shooter and the school.
Asked at a news conference whether Lanza had left any emails or other writings that might explain the rampage, state police Lt. Paul Vance said investigators had found "very good evidence" and hoped it would answer questions about the gunman's motives. Vance would not elaborate.
Officals also said that the suspect forced his way into the school; he was not let in voluntarily.
The tragedy plunged the picturesque New England town of 27,000 people into mourning.
"People in my neighborhood are feeling guilty about it being Christmas. They are taking down decorations," said Jeannie Pasacreta, a psychologist who volunteered her services and was advising parents struggling with how to talk to their children.
Lanza shot his mother, Nancy Lanza, drove to the school in her car with at least three of her guns, and opened fire in two classrooms around 9:30 a.m. Friday, law enforcement officials said, speaking on condition of anonymity.
A custodian ran through the halls, warning of a gunman, and someone switched on the intercom, perhaps saving many lives by letting them hear the chaos in the school office, a teacher said. Teachers locked their doors and ordered children to huddle in a corner, duck under their desks or hide in closets as shots reverberated through the building.
The well-liked principal, Dawn Hochsprung, was believed to be among the dead. A woman who worked at the school was wounded.
Maryann Jacob, a clerk in the school library, was in there with 18 fourth-graders when they heard a commotion and gunfire outside the room. She had the youngsters crawl into a storage room, and they locked the door and barricaded it with a file cabinet. There happened to be materials for coloring, "so we set them up with paper and crayons."
After what she guessed was about an hour, officers came to the door and knocked, but those inside couldn't be sure it was the police.
"One of them slid his badge under the door, and they called and said, `It's OK, it's the police,"' she said.
A law enforcement official speaking on condition of anonymity said investigators believe Lanza attended the school several years ago but appeared to have no recent connection to it. It was not clear whether he held a job.
At least one parent said Lanza's mother was a substitute teacher at the school. But her name did not appear on a staff list. And the official said investigators were unable to establish any connection so far between her and the school.