In one of America’s worst school shootings, gunman Adam Lanza killed 20 children, all first graders aged six or seven, who were shot up to 11 times each.
Alongside the eight boys and 12 girls, he also killed six women, including school head Dawn Hochsprung, before turning the gun on himself.
Mr Obama’s visit to Newtown for an interfaith vigil today will be the fourth time he has travelled to a city after a mass shooting.
The bloodbath brought despair and horror to the smalltown community, 60 miles north-east of New York City, preparing for the Christmas holidays.
Investigators are trying to learn more about the 20-year-old killer who launched his rampage at the school after first killing his mother at their Newtown home.
His girlfriend and another friend are still missing in New Jersey, a police source said.
The father of the gunman has spoken about his family’s struggle to understand what happened.
Peter Lanza said in a statement that “our family is grieving along with all those who have been affected by this enormous tragedy”.
He added: “No words can truly express how heartbroken we are,” and that relatives are “in a state of disbelief and trying to find whatever answers we can”.
Tales have begun to emerge of heroism by teachers and other staff to protect the children.
Young teacher Victoria Soto was shot dead when she put herself between the gunman and her pupils, whom she was trying to hide in a closet, reports said.
Though details of the 27-year-old teacher’s death remain unclear, her cousin, Jim Wiltsie, told ABC News that investigators told his family she was killed while shielding her students from danger.
He said: “She was trying to shield, get her children into a closet and protect them from harm. And by doing that, put herself between the gunman and the children. She lost her life doing what she loved.”
Ms Hochsprung reportedly lunged at Lanza before being shot.
Board of Education chairwoman Debbie Liedlien said administrators were coming out of a meeting when the gunman forced his way into the school, and they ran toward him.
Jeff Capeci, chairman of the town’s legislative council, was asked whether Ms Hochsprung was a hero. He replied: “From what we know, it’s hard to classify her as anything else.”
Maryann Jacob, who worked in the library, told how she led 18 children to safety by crawling with them to a storage room and waiting for police to arrive.
She said they barricaded the door with filing cabinets, only opening it when a police officer slid an identification badge underneath.
Robbie Parker, the father of six-year-old victim Emilie Parker, described her as an “exceptional artist” who was “bright, creative and very loving”.
Fighting back tears, he said: “My daughter Emilie would have been one of the first ones to be standing and giving her love and support to all those victims, because that’s the type of person she is.
“As the deep pain begins to settle into our hearts, we find comfort reflecting on the incredible person Emilie was and how many lives she was able to touch in her short time here on earth.
“Emilie’s laughter was infectious and all those who had the pleasure to meet her would agree that this world is a better place because she has been in it.”
He said his thoughts and prayers go out to relatives of the other victims, including the family of the gunman.
“I want to make sure my family, my wife and my daughters are taken care of,” he said. “If there’s anything I can do to help anybody at any time, then I’d be willing to do that.”
Police in Newtown last night released the names of the 26 people killed in the massacre on Friday at Sandy Hook Elementary School which has rocked the United States and reignited the country’s gun control debate.
Connecticut’s chief medical examiner H Wayne Carver II told a press conference all the children killed were shot more than once, with the ones he examined personally shot between three and 11 times.
“Everybody’s death was caused by gunshot wounds,” he said.
“I have been at this more than a third of a century ... this probably is the worst I have seen, or the worst I know any of my colleagues have seen.”
He added that all of those he had examined so far had injuries sustained by shots from a “long weapon”, reported to be a .223-calibre rifle, with only two people shot at close range.
Friends and family members today described Newtown High School student Lanza variously as intelligent, nerdy, a goth and remote.
His older brother Ryan, 24, who was questioned by police but is not believed to have been involved in the shooting, said his brother had a personality disorder and was “somewhat autistic”.
Police said today they believe the killer forced his way into the building, and added they had found evidence at the crime scenes that could explain his motives.
State Police Lieutenant Paul Vance told a press conference: “Our investigators at the crime scene - the school - and secondarily at the secondary crime scene we discussed, where the female (Lanza’s mother Nancy) was located deceased, did produce some very good evidence in this investigation that our investigators will be able to use in, hopefully, painting the complete picture as to how, and more importantly, why this occurred.”
He confirmed the gunman forced his way into the school, adding: “It is believed he was not voluntarily let into the school at all, that he forced his way into the school, but that is as far as we can go on that.”
Two pistols - a Glock and a Sig Sauer - were found inside the Newtown school, while a rifle was recovered from the back of a car at the site. Officers are currently determining whose they are.
The attack was the latest of several mass shootings in the US this year and carries echoes of the Dunblane massacre, where 16 schoolchildren and one teacher were killed by gunman Thomas Hamilton in the Scottish town in 1996.
It approached the deadly scale of the Virginia Tech university massacre in 2007 that left 32 dead.
Another alleged killer, James Holmes, 24, is awaiting trial charged with 24 counts of murder and 116 counts of attempted murder after the “Batman” cinema shootings in Aurora, Colorado, in June which left 12 people dead and 58 wounded.
In another incident today a gunman was shot dead by police after opening fire in St Vincent’s Hospital in Birmingham, Alabama, injuring an officer and two employees.
Messages of condolence flooded in for those killed in Newtown, led by the Queen and Prime Minister David Cameron in the UK, with others from figures including Pope Benedict XVI.