The gunman in America's worst school shooting was carrying hundreds of rounds of ammunition during his killing spree, police said.
Adam Lanza, 20, opened fire with a high-powered rifle inside Sandy Hook Elementary School on Friday morning, killing 26 people. Twenty of the victims were children, all aged six or seven.
Police said he used a Bushmaster AR-15 type weapon against most victims, but killed himself with a handgun. A shotgun was left in his car outside the school.
"There was a lot of ammo, a lot of clips," State Police Lt. Paul Vance said. "Certainly a lot of lives were potentially saved."
Connecticut Governor Dan Malloy said earlier that the gunman committed suicide as the first police and paramedics closed in.
The assault on the school began when Lanza blasted his way through a locked glass door and climbed through, Mr Malloy said.
"He shot his way into the building. He penetrated the building by literally shooting an entrance into the building. That's what an assault weapon can do for you," he said.
"He discharged to make an opening and then went through it, went to the first classroom ... went to the second classroom.
"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."
The school had just installed a new security door where visitors could be viewed by video camera before being buzzed in.
Before arriving at the school, Lanza shot dead his mother Nancy Lanza at the home they shared.
The coroner confirmed on Sunday that Nancy Lanza had been shot multiple times. Lanza shot himself in the head.
Mr Malloy said there was still little clue to Lanza's motivation, but that a picture of his mental state would eventually emerge. So far, police have not said whether they found a suicide note or any other documents.
"Clearly he was troubled. You have to be deranged to carry out this kind of crime," Mr Malloy said.
"This was a troubled individual ... I'm sure we'll come to know more about him, his problems, his family."
All six adults killed at the school were women. Of the 20 children, eight were boys and 12 were girls.
After police released the names of the gunman's 27 victims, one father paid an emotional tribute to his murdered six-year-old daughter.
Robbie Parker said his final conversation with Emilie was in Portuguese, the language he was helping to teach her.
"She told me 'good morning' and asked how I was doing, and I said that I was doing well," he told reporters.
"She said that she loved me, and I gave her a kiss and I was out the door."
Headteacher Dawn Hochsprung and school psychologist Mary Sherlach both died as they tried to confront the gunman.
Ms Hochsprung is also believed to have switched on a loudspeaker system in the school to alert students and staff to the danger.
"She was just an amazing woman ... the kids loved her. It's a huge loss for our school and our town," said assistant librarian Maryanne Jacobs.
Another hero was said to be first-grade teacher Vicki Leigh Soto, 27, described by police as someone who "put herself between the kids and the gunman's bullets".
Her body was found huddled with the students in a classroom closet, according to The Wall Street Journal.