Police say 27 people were killed in the shooting at a Connecticut elementary school, including the gunman, and one person died at another scene.
The dead at the school include 20 children.
The gunman opened fire Friday morning inside a school where his mother worked. He blasted his way through the building as young students cowered helplessly in classrooms while their teachers and classmates were shot.
The gunman killed himself. The state's governor says someone who lived with him also died.
Young students crying and looking frightened were escorted by adults through a parking lot in a line after the shots rang out in Newtown, 60 miles northeast of New York City.
The attack comes less than two weeks before Christmas and appears to be the nation's second-deadliest school shooting, exceeded only by the Virginia Tech massacre in 2007.
A law enforcement official says the suspect in the Connecticut school shootings is 20-year-old Adam Lanza, the son of a teacher at the school where the shootings occurred. A second law enforcement official says the boy's mother, Nancy Lanza, is presumed dead.
The first official says Adam Lanza's older brother, 24-year-old Ryan, of Hoboken, N.J., is being questioned by police. An earlier report from a law enforcement official mistakenly transposed the brothers' first names.
Both officials spoke on the condition of anonymity because they were not authorized to speak on the record about the developing criminal investigation.
The first official said Adam Lanza is dead from a self-inflicted gunshot wound.
Family members are relaying what children told them about the shooting at Sandy Hook Elementary School in Newtown, Connecticut.
A 6-year-old told his father that he was in his classroom when a gunman burst in and shot the teacher. Robert Licata says his son "grabbed a bunch of his friends and ran out the door." Licata says the shooter didn't say a word.
Stephen Delgiadice says his 8-year-old daughter heard two big bangs and teachers told her to get in a corner. His daughter is fine.
He says the shooting is alarming because his family always considered Newtown to be the safest place in America.
Seventeen-year-old Mergim Bajraliu heard the gunshots echo from his home and raced to check on his 9-year-old sister at the school. He says his sister heard a scream come over the intercom at one point. And he says teachers were shaking and crying as they came out of the building.
As a father, President Barack Obama says, he's grieving for the victims of today's school shooting in Connecticut.
His remarks to the nation from the White House today were emotional ones, as Obama wiped his eyes and had to pause for several seconds to keep his composure.
He said, "Our hearts are broken today." Obama said the victims were "beautiful, little kids" who "had their entire lives ahead of them" -- and he recited future milestones lost: "birthdays, graduations, weddings, kids of their own."
Obama called for "meaningful action" to prevent such shootings, but he did not say what that action should be. He ordered U.S. flags be flown at half-staff through Tuesday.
As he spoke, two senior aides standing nearby cried and held hands.
Obama, who began his comments with no greeting, ended them with words of Scripture, and walked away in silence.
Shortly before speaking, Obama ordered that U.S. flags be flown at half-staff on public grounds through Tuesday.