The search for answers began Saturday after authorities in Newtown, Connecticut, identified all of the victims killed in Friday's school shooting.
President Barack Obama urged Americans to join in solidarity in his weekly address, but stopped short of calling for stricter gun control.
The bodies of the 20 children and six adults gunned down Friday morning by 20-year-old Adam Lanza had been removed from Sandy Hook Elementary School, and mourners were gathered at the firehouse nearby, NBC News reported.
“(Parents) were wondering whether the children knew what was happening to them, whether they were afraid,” Monsignor Robert Weiss told NBC.
Authorities said Lanza shot and killed his mother, Nancy Lanza, at her home in Newtown, then took three of her guns and drove her car to the school.
It appeared he broke some glass near the entrance to the 600-student school to get inside.
Lanza, said to have a personality disorder, then opened fire in the hallways and several classrooms, gunning down 26 adults and children before taking his own life, CBS News reported.
On Friday night, thousands packed St. Rose of Lima Catholic Church and other nearby churches for community vigils while gun-control advocates held a candlelight vigil outisde the White House.
The most prominent calling for reforms was New York Mayor Michael Bloomberg, who declared pointedly in a statement: "Calling for 'meaningful action" is not enough. We need immediate action. We have heard all the rhetoric before," according to The Associated Press.