“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 television's “This Week.”
Authorities said they found hundreds of unused bullets at the Sandy Hook Elementary 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 the type designed to break up inside a victim's body and inflict the maximum amount of damage, tearing apart bone and tissue.
Newtown officials couldn't say whether Sandy Hook Elementary School would ever reopen. The school district was considering sending surviving students to an empty school in nearby Monroe. But for many parents, it was much too soon to contemplate resuming school-day routines.
“We're just now getting ready to talk to our son about who was killed,” said Robert Licata, the father of a boy who was at the school during the shooting but escaped harm. “He's not even there yet.”
Jim Agostine, superintendent of schools in nearby Monroe, said plans were being made for students from Sandy Hook to attend classes in his town this week.
The road ahead for Newtown was clouded with grief.
“I feel like we have to get back to normal, but I don't know if there is normal anymore,” said Kim Camputo, mother of two children, ages 5 and 10, who attend a different school. “I'll definitely be dropping them off and picking them up myself for a while.”
Also Sunday, a Connecticut official said the gunman's 52-year-old mother, Nancy Lanza, was found dead in her pajamas in bed in the home they shared, shot four times in the head with a .22-caliber rifle.
The killer then went to the school Friday morning with guns he took from his mother, got inside by breaking a window and began blasting his way through the building.
All the victims at the school were shot with the rifle, at least some of them up close, and all were apparently shot more than once, Chief Medical Examiner Dr. H. Wayne Carver said.
There were as many as 11 shots on the bodies he examined. Lanza died of a gunshot wound to the head from a 10 mm gun, said the same official who described the scene at the mother's house.
Amid the confusion and sorrow, stories of heroism emerged, including an account of the principal Dawn Hochsprung, 47, and the school psychologist, Mary Sherlach, 56, rushing toward Lanza in an attempt to stop him. Both died.
There was also 27-year-old teacher Victoria Soto, whose name has been invoked as a portrait of selflessness. Investigators told relatives she was killed while shielding her first-graders from danger.
She reportedly hid some students in a bathroom or closet, ensuring they were safe, a cousin, Jim Wiltsie, told ABC News.
“She put those children first. That's all she ever talked about,” a friend, Andrea Crowell, told The Associated Press. “She wanted to do her best for them, to teach them something new every day.”
Federal agents have concluded that 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.
