The gunman in the Connecticut shooting rampage was carrying an arsenal of hundreds of rounds of especially deadly ammunition — enough to kill just about every student in the school if given enough time, authorities said Sunday, raising the chilling possibility that the bloodbath could have been even worse.
On Sunday night, President Barack Obama told mourners at a vigil that the nation is failing to keep its children safe. He pledged to seek change in memory of the six adults and 20 boys and girls ages 6 and 7 who were killed in the second-deadliest school shooting in U.S. history.
"What choice do we have?" Obama said. "Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard?"
The gunman, Adam Lanza, shot himself in the head just as he heard police drawing near to the classroom where he was slaughtering helpless children, but he had more ammunition at the ready in the form of multiple, high-capacity clips, each capable of holding 30 bullets, officials said Sunday.
Gov. Dannel Malloy said the shooter decided to kill himself about 10 minutes into the attack.
"We surmise that it was during the second classroom episode that he heard responders coming and apparently at that decided to take his own life," Malloy said on ABC's This Week.
Police said they found hundreds of unused bullets at the school, which enrolled about 450 students in kindergarten through fourth grade.
"There was a lot of ammo, a lot of clips," said state police Lt. Paul Vance. "Certainly a lot of lives were potentially saved."
The chief medical examiner has said the ammunition was a type designed to expend its energy in the victim's tissues and stay inside the body to inflict the maximum amount of damage.
In his speech, Obama said in the coming weeks he would use "whatever power this office holds" to engage with law enforcement, mental health professionals, parents and educators in an effort to prevent more tragedies like Newtown.
He promised to lead a national effort but left unclear what it would be and how much it would address the explosive issue of gun control.
Obama closed his remarks by slowly reading the first names of each of the 26 victims.
"God has called them all home," he said. "For those of us who remain, let us find the strength to carry on and make our country worthy of their memory."
Cries and sobs filled the room.
"That's when it really hit home," said Jose Sabillon, who attended the interfaith memorial with his son, Nick, a fourth-grader who survived the shooting unharmed.
Inside the room, children held stuffed teddy bears and dogs. The smallest kids sat on their parents' laps.
Obama conceded that none of his words would ease the sorrow. But he declared to the community of Newtown: "You are not alone."
Privately, Obama told the governor that Friday was the most difficult day of his presidency.
The president first met privately with families of the victims and with the emergency personnel who responded to the shootings. The gathering happened at Newtown High School, the site of Sunday night's interfaith vigil, about a mile and a half from where the shootings took place.
Police and firefighters got hugs and standing ovations when they entered. So did Obama.
"We needed this," said the Rev. Matt Crebbin, senior minister of the Newtown Congregational Church. "We needed to be together to show that we are together and united."
In the investigation, a Connecticut official said the gunman's mother, Nancy Lanza, 52, was found dead in her pajamas in bed, shot four times in the head with a .22-caliber rifle. The killer then went to the school with guns he took from his mother, blasted his way inside and began spraying the children with bullets.
Federal agents have concluded that Adam Lanza visited an area shooting range, but they do not know whether he actually practiced shooting there.
Ginger Colburn, a spokeswoman for the federal Bureau of Alcohol, Tobacco and Firearms, would not identify the range or say how recently he was there.
Agents also determined that Lanza's mother visited shooting ranges several times, but it's still not clear whether she brought her son to the range or whether he ever fired a weapon there, Colburn said.
Investigators have offered no motive for the shooting, and police have found no letters or diaries that could shed light on it. They believe Lanza attended Sandy Hook many years ago, but they couldn't explain why he went there Friday.
Authorities said Lanza had no criminal history, and it was not clear whether he had a job.
At least one law enforcement official has said Lanza had been diagnosed with Asperger's, a mild form of autism often characterized by social awkwardness.
People with the disorder are often highly intelligent. While they can become frustrated more easily, there is no evidence of a link between Asperger's and violent behavior, experts say.