The shattered community of Newtown is holding its first two funerals including one for the youngest victim.
Meanwhile education officials were unsure if the school where the massacre happened would ever reopen. Nervous pupils and teachers across the country returned to classrooms under tighter security.
Further details on just what happened during Friday's shooting were "too difficult to discuss," said Connecticut state police lieutenant Paul Vance.
The first funerals were planned for six-year-olds Jack Pinto and Noah Pozner, who had his birthday two weeks ago.
Investigators have offered no motive for the shooting, and the community struggled to comprehend what drove 20-year-old Adam Lanza to shoot dead his mother at home in bed Friday morning, drive her car to the school and murder six adults and 20 children.
"I can tell you it broke our hearts when we couldn't save them all," Lt. Vance said. He said two adults who were injured were recovering.
He also said police may hold the school and the Lanza home for months as the investigation continues.
Newtown officials could not say whether Sandy Hook Elementary would ever reopen. Plans were made to send surviving pupils to a former school building in a neighbouring town.
Newtown police Lt. George Sinko said he "would find it very difficult" for students to return to the same school. But, he added, "We want to keep these kids together. They need to support each other."
Divorce paperwork made public on Monday showed that Lanza's mother had the authority to make all decisions regarding his upbringing. It makes no mention of any mental health issues regarding Lanza. The paperwork says the marriage broke down "irretrievably." The divorce was finalised in September 2009, when Adam Lanza was 17.