The Queen and Prime Minister David Cameron have led UK tributes to the 27 victims of one of the worst mass school shootings in American history, as more information came to light about the man believed to have carried out the atrocity.
Suspected gunman Adam Lanza shot dead 18 children aged between five and 10 and six adults at Sandy Hook Elementary School in Connecticut, where his mother Nancy was a teacher, before killing himself. Two other children shot at the scene died in hospital later.
School principal Dawn Hochsprung, who had been in charge since 2010, was among the adults shot dead by the gunman, an official told reporters.
Several publications report she wrote a letter before the school year outlining new safety measures - including locked doors during school hours.
Lanza's older brother Ryan, 24, of Hoboken, New Jersey, who is being questioned by police but is not believed to have been involved, told investigators Adam, who lived with their mother in Connecticut, was believed to suffer from a personality disorder and be "somewhat autistic".
In a message sent to President Barack Obama, the Queen said she was "deeply shocked and saddened" to hear of the shootings.
The Prime Minister later issued a statement, saying he was "shocked and deeply saddened" by events at the school.
"It is heartbreaking to think of those who have had their children robbed from them at such a young age, when they had so much life ahead of them," he said.
Pope Benedict XVI became the latest figure to offer his condolences to the people affected by the shooting.
A message sent to the catholic diocese of Bridgeport in Connecticut by Cardinal Tarcisio Berton, the Vatican secretary of state, said: "The Holy Father was promptly informed of the shooting at Sandy Hook Elementary School in Newtown and he has asked me to convey his heartfelt grief and the assurance of this closeness in prayer to the victims and their families, and to all affected by the shocking event."