With so much grieving left to do, many of Newtown's 27,000 people wondered whether life could ever return to normal. And as the workweek was set to begin, parents pondered whether to send their own children back to school.
Gov. Dannel Malloy said the shooter decided to kill himself when he heard police closing in 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."
Authorities said they found multiple 30-round magazines and hundreds of unused bullets at the school, which enrolled about 670 students.
"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 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, where the shooter killed 20 children and six adults, would ever reopen.
"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 mother 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, got inside by breaking a window and began blasting his way through the building.
As President Barack Obama prepared to visit later Sunday and churches opened their doors, federal agents checked out dozens of gun stores and shooting ranges across Connecticut, chasing leads they hoped would cast light on Lanza's life.
Malloy offered no possible motive for the shooting, and police have found no letters or diaries that could shed light on it.
School officials were discussing how to send survivors back to class, but Newtown police Lt. George Sinko said he "would find it very difficult" for students to return to the school. But, he added: "We want to keep these kids together. They need to support each other."
Jennifer Waters, who at 6 is the same age as many of the dead but attends another school, came to Mass at Saint Rose of Lima Roman Catholic church with lots of questions.
"The little children are they with the angels?" she asked her mother.
Joan Waters assured her daughter that they were, then hushed the child as services continued with boxes of tissues placed in each pew and window sill.
An overflow crowd of more than 800 people packed the church where eight children will be buried this week. Lanza and his mother also attended the church. Spokesman Brian Wallace said the diocese has yet to be asked to provide funerals for either.
In his homily, the Rev. Jerald Doyle tried to answer the question of how parishioners could find joy in the holiday season with so much sorrow.
"You won't remember what I say, and it will become unimportant," he said. "But you will really hear deep down that word that will finally and ultimately bring peace and joy. That is the word by which we live. That is the word by which we hope. That is the word by which we love."
Amid the confusion and sorrow, stories of heroism emerged, including an account of Principal Dawn Hochsprung and school psychologist Mary Sherlach, who rushed toward Lanza in an attempt to stop him. Both were killed.
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. She 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."
The rifle used was a Bushmaster .223-caliber, a civilian version of the military's M-16 and a model commonly seen at marksmanship competitions. It's similar to the weapon used in the 2002 sniper killings in the Washington, D.C., area and in a recent shopping mall shooting in Oregon.
Versions of the AR-15 were outlawed in the United States under the 1994 assault weapons ban. That law expired in 2004, and Congress, in a nod to the political clout of the gun-rights lobby, did not renew it.
Investigators have said they believe Adam 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.
A law enforcement official, speaking on condition of anonymity because the person was not authorized to discuss the unfolding investigation, 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.
Associated Press writers Michael Melia and Pat Eaton-Rob in Newtown and Brian Skoloff in Southbury contributed to this report.
No danger at Conn. church after phoned threat
Newtown, Conn. • Worshippers hurriedly left a church Sunday when someone phoned in a threat as parishioners remembered 20 children and six adults who were massacred at an elementary school, but police later said nothing dangerous was found.
The threat interrupted a busy Mass and touched off a large police response days after the worst massacre of school-age children in U.S. history.
Halfway through the noon service at the St. Rose of Lima Church, the priest stopped and said, "Please, everybody leave. There is a threat," said worshipper Anna Wood of Oxford, Conn.
At least a dozen police in camouflage SWAT gear and carrying guns soon arrived. An Associated Press photographer saw police leave carrying something in a red tarp. Guns drawn, they searched the church and adjacent buildings.
Deborah Metz, a Trumbull police officer on the scene, gave the all-clear after about an hour. Police said the church would be on lockdown for the rest of the day.
Brian Wallace, spokesman for the diocese, said someone called and "threatened to disrupt the mass."
Gunman Adam Lanza, his mother and eight of the child victims attended St. Rose of Lima. It is a Roman Catholic Church with an adjacent school, which Lanza attended briefly.
The church hosted overflow crowds at all three morning Masses Sunday.