At the end of a tragic news day, the question remains: how could this happen? and why? As with other mass murders that have stained US history, the answer could lie in a mentally unstable shooter with few friends to pick up warning signs, and access to high-powered guns.
The loner suspected of killing more than two dozen people at a school in the US state of Connecticut was an honours student who lived in a prosperous neighbourhood with his mother, a grade school teacher who liked to host dice games and decorate the house for the holidays, AP reports.
Personal details about Adam Lanza are dribbling out, but he left few footprints. Described by his brother as having a personality disorder, the suspected shooter had no Facebook page and did not even appear in his high school yearbook; his spot on the page said "Camera shy", The New York Times reported.
Described by former classmates as intelligent but socially inept, authorities are reportedly examining whether Lanza's disorder was Asperger's syndrome, a high functioning form of autism. Police are still searching for a motive.
Candle in the wind ... a child protects candles during a vigil outside the White House. Photo: AFP
Hundreds of grief-stricken Newtown residents gathered for a vigil on Friday night in memory of the children and staff killed in the shooting rampage.
Twenty-six candles - one for each of the victims at the school - flickered on the altar at the St. Rose of Lima Roman Catholic church, which was filled to capacity. Scores spilled outside holding hands in circles in the cold night air, saying prayers and singing "Silent Night", AP reports.
Monsignor Robert Weiss said: "These 20 children lit up this community better than all these Christmas lights we have. ... There are a lot brighter stars up there tonight because of these kids."
People gather for a prayer vigil at St Rose Church following an elementary school shooting in Newtown. Photo: AFP
World leaders have expressed shock and horror at the tragedy. UN chief Ban Ki-moon, British Prime Minister David Cameron, European Union diplomacy chief Catherine Ashton, Queen Elizabeth II and others have variously described the shooting as "heinous and unthinkable", "horrendous", "horrific" and "heartbreaking".
Fairfax correspondent Nick O'Malley arrived in Newtown a short time ago, and described the scene: "People are gathering in restaurants and coffee shops; basically they don't want to be alone," he said.
O'Malley described Newtown as a "beautiful town" and said it was festooned with Christmas lights and the lights from all the TV networks doing their outside broadcasts.
It has just gone 10:45pm in Newtown and things are starting to quieten down, with police scheduled to hold their next briefing at 8am local time.
Sandy Hook Elementary School, which is about a five-minute drive from the centre of town, remains cordoned off by police. It is not known whether remains of some of the victims are still inside.
- Read O'Malley's story: Town mourns young lives extinguished too soon
People grieve outside the overflow area of a vigil at the Saint Rose of Lima church in Newtown, Connecticut. Photo: Reuters
The White House continues to be vague about whether tighter gun laws are in the offing following President Barack Obama's claim that "meaingful action to prevent more tragedies like this" was on the way. White House spokesman Jay Carney said the administration did not want to politicise a tragedy when asked for more detail of any new initiatives.
Liberal Democrats are already pushing for tighter laws but despite a long history of school shootings Republicans have yet to be swayed that further gun control is necessary.
"'That's one thing I hope doesn't happen,'' said Rep. Mike Rogers, a senior Michigan Republican who is a former FBI agent, according to The New York Times. ''That's certainly the lowest common denominator. What is the more realistic discussion is, how do we target people with mental illness who use firearms?''
A law enforcement official said guns legally purchased by shooter Adam Lanza's mother matched the models of guns used in Friday's rampage. Police found Lanza dead in a classroom along with two guns, a Glock and Sig Sauer; another gun, a Bushmaster, was found in his car.
Supporters of gun control legislation hold candles during a rally in front of the White House after the shooting. Photo: Reuters
Lieutenant Paul Vance of Connecticut State Police described the scene at the school as "horrific". "Between our mutual experience we've never seen anything like this - it's as heart-wrenching for us as it is for the families," he told reporters.
He said the murdered children would be identified on the weekend after families had been properly notified and "positive IDs" were confirmed.
Another hero teacher story has emerged from the second deadliest school shooting massacre in US history.
The Daily Mail reports that music teacher Maryrose Kristopik saved 15 children during the shooting by barricading them into a closet, as gunman Adam Lanza was outside the door screaming "Let me in! Let me in!".
The paper quoted an unnamed mother, in her 40s, whose nine-year-old son was among the children, saying: "I want to thank her. She saved their lives."
Another parent, Brenda Lebinski, said her eight-year-old daughter was safe thanks to the "hero" teacher.
Maryrose Kristropik conducting the choir at assembly in a picture tweeted by murdered principal Dawn Hochsprung.
More reports are coming in from children who witnessed the shooting at Sandy Hook Elementary School.
Bloomberg reports that C.J. Hoekenga, a Sandy Hook fourth-grader, was in music class watching The Nutcracker when he heard bangs, heavy breathing and then gunshots. His teacher told them to get into a closet, the youngster said.
''At first I thought it was practice,'' C.J. said. ''Then we realised it wasn't.''
He and classmates said prayers until a police officer arrived. They then exited single-file and ran to a nearby fire station, he said.''I'm relieved that most of the children got out and the man behind this is dead,'' C.J. said.
The New York Times quoted a nine-year-old boy who said he was in the gymnasium when the shooting erupted.
''We were in the gym, and I heard really loud bangs,'' said the boy, as he stood shivering and weeping outside the school with his father's arms draped around him.
''We thought that someone was knocking something over. And we heard yelling and we heard gunshots. We heard lots of gunshots. We heard someone say, 'Put your hands up.' I heard, 'Don't shoot.' We had to go into the closet in the gym. Then someone came and told us to run down the hallway. There were police at every door, there were lots of people crying and screaming.''
A boy weeps as he is told what happened Sandy Hook Elementary School. Photo: Reuters
Year 1 teacher Kaitlin Roig has told US television reporter Diane Sawyer how she hid her class in a bathroom to protect them from the gunfire.
"I just knew we had to get in there, I just kept telling them it's going to be OK," Ms Roig said as she fought back tears.
She recounted how she pulled a bookshelf in front of the door before closing herself and the children inside.
"I was so afraid that if he did come in and he would hear us he would just start shooting the door."
She said the children were extremely brave and she told them: "There are bad guys out there now; we have to wait for the good guys."
When the children became distressed she told them to "show me your smile". She told each of the children that she loved them "because I thought that was the last thing they were ever going to hear".
"I don't know if that's ok .. [for] teachers [to say that] .. but I wanted that to be one of the last things they heard, not the gunfire in the hallway."
"I didn't think we were going to live" ... teacher Kaitlin Roig.
ABC News has spoken to a relative of 20-year-old suspected shooter Adam Lanza who said he was "obviously not well". A family friend said he was "not connected with the other kids".
Police said Adam Lanza shot his mother in the family home before taking her car and several weapons and going on his deadly rampage at the elementary school, killing 20 children and six adults.
Alleged Sandy Hook Elementary shooter Adam Lanza is seen in this 2005 photo. Photo: ABCNews US
Ryan Lanza, the 24-year-old brother of suspected shooter Adam Lanza, told authorities that his brother was believed to have suffered from a personality disorder and was "somewhat autistic", a law enforcement official told AP.
Ryan, who lives in Hoboken, New Jersey, was initially mistakenly identified by a law enforcement official as the shooter. Officials now say Ryan was extremely cooperative with police during questioning and while he is not believed to have had any involvement in the shooting, investigators are still searching his computers and phone records.
Ryan Lanza is taken in for questioning in this frame grab provided by WCBS in New York. Photo: AP Photo/WCBS-TV
A second victim killed at the school has been identified as 56-year-old Mary Sherlach, who worked at Sandy Hook Elementary School for 20 years since 1994.
According to her biography on the school's website she was married to financial consultant Bill Sherlach and was a mother of two daughters, who are in their 20s.
"We enjoy traveling and spending time at our lake home in the Finger Lakes in upstate New York," the bio, quoted by New York Daily News, stated. "My hobbies include gardening, reading, and the theater."
People take part in a candlelight vigil in Times Square, for the victims of the Sandy Hook School shooting Photo: Reuters
Mayors Against Illegal Guns has started a petition to pressure President Barack Obama to change US gun laws.
New York City mayor Michael Bloomberg said in a statement that Obama should send a bill to Congress to fix the problem as "not even kindergarteners learning their ABC's are safe".
"We heard after Columbine that it was too soon to talk about gun laws. We heard it after Virginia Tech. After Tucson and Aurora and Oak Creek. And now we are hearing it again," he said. "For every day we wait, 34 more people are murdered with guns."
Boston Mayor Thomas Menino said: "Now is the time for a national policy on guns that takes the loopholes out of the laws, the automatic weapons out of our neighborhoods and the tragedies like today out of our future."
Principal Dawn Lafferty Hochsprung, killed in the shooting at her Connecticut elementary school, recently installed a new security system to ensure student safety, CNN reports.
She wrote in a letter to parents that every visitor to the Sandy Hook Elementary School would be required to ring the doorbell at the front entrance after the doors locked at 9:30am, and a staff member would use a visual monitoring system to determine entry.
Visitors would then have to report directly to the main office and sign in, showing photo identification if staff didn't recognise them.
Sandy Hook Elementary School principal Dawn Hochsprung. Photo: Reuters
Early reports suggested shooter Adam Lanza killed his father at home before heading to the school and beginning his rampage. Police have confirmed a body was found at a home believed to be owned by his mother Nancy Lanza, but it doesn't appear to be that of the father Peter Lanza.
Connecticut Post is now reporting Peter Lanza, a vice president of taxes for GE Energy Financial Services, arrived home minutes after police left and politely asked a Hearst Connecticut Media Group reporter: "Is there something I can do for you?" after rolling down the window of his blue Mini Cooper. He reportedly did not know his address had been linked to the shooting.
AP has just reported that mother Nancy Lanza was killed at the home, not at the school as earlier reported.
The story is dominating social media and many are using the hashtag #prayfornewtown to express their grief, condolences and revulsion. Both that hashtag and "Connecticut" are trending on Twitter.
Brogan Hume summed up the sentiment of those reacting online.
How do we talk to our children about what happened at Sandy Hook Elementary today? How do we send our kids to school next week?
Kavita Varma-White, contributor to Today.com, quotes psychiatrist Dr. Gail Saltz saying it's a tough but necessary discussion. Click here to read more.
Kids around the world will be asking the question - is it safe to go to school? Photo: Reuters
The massacre of 28 people including 20 young children, the second highest death toll ever in a US shooting after the 32 killed in the Virginia Tech shootings in 2007, has reignited the debate over US gun laws.
Until now there have been few signs of change in the laws but after the latest massacre, President Barack Obama appeared on television with tears in his eyes to make an emotional plea for "meaningful action".
"As a country we have been through this too many times," Obama said, mentioning earlier massacres in Colorada, Oregon and Wisconson.
White House spokesman Jay Carney earlier refused to be drawn on the political fallout, telling reporters it was a day to "feel enormous sympathy for families that are affected".
But AP reports congressman Jerrold Nadler, a Democrat, immediately responded: ''If now is not the time to have a serious discussion about gun control and the epidemic of gun violence plaguing our society, I don't know when is.''
"Yet another unstable person has gotten access to firearms and committed an unspeakable crime against innocent children. We cannot simply accept this as a routine product of modern American life,'' he said.
Prime Minister Julia Gillard has given her thoughts on the tragedy in a press release. This is what she has said.
"Australia grieves with America today following the mass shooting of primary school children and teachers in Connecticut.
"Like President Obama and his fellow Americans, our hearts too are broken.
"We share America’s shock at this senseless and incomprehensible act of evil.
"As parents and grandparents, as brothers and sisters, as friends of the American people, we mourn the loss of children, aged only five to ten years, whose futures lay before them.
"We mourn the loss of brave teachers who sought only to lead their students into that future but were brutally murdered in a place of refuge and learning.
"Our thoughts today are with the people of America.
"We hold in our hearts the families who have lost loved children and who face grief beyond measure. We think of the families of the teachers.
"And we hope for the recovery of those injured in body and spirit."
Prime Minister Julia Gillard. Photo: Andrew Meares
Newtown is home to 27,000 residents, is about 70 kilometres southwest of Hartford, the state capital, and 110 kilometres northeast of New York City.
"It’s absolutely beautiful ... wonderful. It’s quiet. Nothing ever goes on here," local insurance agent Adina Tornow has told USA Today.
The town’s beauty "has been tarnished because of this", Tornow said.
SIte of the masscre ... this aerial photo shows Sandy Hook Elementary School in Newtown, Connecticut. Photo: AP
The pictures coming out from Newtown capture the raw emotion of those caught up in the tragedy.
US President Barack Obama wiped away tears and struggled to compose himself as he mourned the dead in the Connecticut school shooting, and promised "meaningful" action to stop gun tragedies.
"The majority of those who died today were children, beautiful little kids between the ages of five and ten years old," Obama said.
"They had their entire lives ahead of them, birthdays, graduations, weddings, kids of their own."
Visibly upset ... US President Barack Obama. Photo: Reuters
Our US correspondent Nick O'Malley has filed a comprehensive wrap of what we know so far. Click here for the latest news
Massacre ... tearful children are taken away from the school. Photo: Reuters
At least 26 people, including up to 20 children between the ages of five and 10, have been killed in a mass shooting at the Sandy Hook primary school in Newtown, a small town in rural Connecticut.
The gunman, found dead at the scene, was identified by a US law enforcement official as 20-year-old Adam Lanza, who killed his father at home before driving to the school and killing his mother, Nancy Lanza, who worked there, along with many of her young students.
His brother Ryan Lanza, 24, who was initially mistakenly identified by police as the shooter, has been questioned.
School shooting horror ... a young girl cries outside the school. Photo: AP