Adam Lanza's 24-year-old brother, Ryan, of Hoboken, N.J., was being questioned, but the law enforcement official who said that Adam Lanza possibly had a personality disorder said Ryan Lanza was not believed to have played any role in the rampage.
Investigators searched Ryan Lanza's computers and phone records, but he told law enforcement he had not been in touch with his brother since about 2010.
At one point, a law enforcement official mistakenly identified the gunman as Ryan Lanza. Brett Wilshe, a friend of Ryan Lanza's, said Lanza told him the gunman might have had his brother's identification. Ryan Lanza has a Facebook page that posted updates Friday afternoon that read, "It wasn't me'' and "I was at work.''
Stephen Delgiadice said his 8-year-old daughter was in the school and heard two big bangs. Teachers told her to get in a corner, he said.
"It's alarming, especially in Newtown, Connecticut, which we always thought was the safest place in America," he said. His daughter was fine.
Theodore Varga said he was in a meeting with other fourth-grade teachers when he heard the gunfire, but there was no lock on the door.
He said someone turned on the public address system so that "you could hear people in the office. You could hear the hysteria that was going on. I think whoever did that saved a lot of people. Everyone in the school was listening to the terror that was transpiring."Friday night, hundreds of people packed a Newtown church and stood outside in a vigil for the victims. People held hands, lit candles and sang "Silent Night'' at St. Rose of Lima church.
Anthony Bloss, whose three daughters survived the shootings, said they are doing better than he is. "I'm numb. I'm completely numb,'' he said at the vigil.
"Our hearts are broken today," a tearful President Obama said at the White House as he struggled to maintain composure. He called for "meaningful action" to prevent such shootings. "As a country, we have been through this too many times," he said.
Mergim Bajraliu, 17, heard the gunshots echo from his home and ran to check on his 9-year-old sister at the school. He said his sister, who was fine, heard a scream come over the intercom at one point. He said teachers were shaking and crying as they came out of the building.
"Everyone was just traumatized," he said.
Mary Pendergast said her 9-year-old nephew was in the school at the time of the shooting but wasn't hurt after his music teacher helped him take cover in a closet.
On Friday afternoon, family members were led away from a firehouse that was being used as a staging area, some of them weeping. One man, wearing a T-shirt without a jacket, put his arms around a woman as they walked down the middle of the street, oblivious to everything around them.
Another woman with tears rolling down her face walked by carrying a car seat with a young infant inside and a bag that appeared to have toys and stuffed animals.
"Evil visited this community today and it's too early to speak of recovery, but each parent, each sibling, each member of the family has to understand that Connecticut -- we're all in this together. We'll do whatever we can to overcome this event," Gov. Dannel Malloy said.
Adam Lanza and his mother lived in a well-to-do part of Newtown where neighbors are doctors or hold white-collar positions at companies such as General Electric, Pepsi and IBM.
At least three guns were found -- a Glock and a Sig Sauer, both pistols, inside the school, and a .223-caliber rifle in the back of a car, authorities said. A law enforcement official said some of the guns used in the attack might have belonged to Lanza's mother, who legally owned five weapons.
The shootings instantly brought to mind episodes such as the Columbine High School massacre that killed 15 in 1999 and the July shootings at a movie theater in Aurora, Colo., that left 12 dead.
"You go to a movie theater in Aurora and all of a sudden your life is taken," Columbine principal Frank DeAngelis said. "You're at a shopping mall in Portland, Ore., and your life is taken. This morning, when parents kissed their kids goodbye knowing that they are going to be home to celebrate the holiday season coming up, you don't expect this to happen. I think as a society, we need to come together."
He added: "It has to stop, these senseless deaths."
Obama's comments on the tragedy amounted to one of the most outwardly emotional moments of his presidency.
"The majority of those who died were children -- beautiful little kids between the ages of 5 and 10 years old," Obama said.
He paused for several seconds to keep his composure as he teared up and wiped an eye. Nearby, two aides cried and held hands as they listened to Obama.
"They had their entire lives ahead of them -- birthdays, graduations, wedding, kids of their own," Obama continued about the victims. "Among the fallen were also teachers, men and women who devoted their lives to helping our children."