By RACHEL QUIGLEY
Adam Lanza, 20, was carrying a .223 rifle and two handguns when he entered the Sandy Hook Elementary school shortly after 9.30am and started gunning people down.
Witnesses say he was going from room-to-room shooting people after first killing the principal and psychologist execution style and then going to his mother Nancy's kindergarten class where he continued his killing spree.
Officials said most of the slaughter occurred in two classrooms, and one entire class is unaccounted for. One witness told WCBS: '(Police) just told us everyone presumed missing is in the school and they are dead.'
Students described being ushered from their classrooms hand-in-hand, with their eyes closed, to the safety of a nearby fire station as police converged on the school.
Adam's brother Ryan, 24, who was originally thought to have been the shooter, is being questioned by police after he was arrested at his home in Hoboken, New Jersey.
He was on a bus on his way home from work when he was being named as the gunman and posted on Facebook that it wasn't him. He told a friend he believed his mentally disabled brother did it.
The gunman's father Peter Lanza, who is separated from his wife, lives in Stamford, Connecticut, and declined to comment this evening after police performed a welfare check.
The President addressed a stunned nation fiver hours after the shooting and openly wept as he spoke of the mindless shooting saying: 'Our hearts are broken today'.
Seldom has a head of state expressed greater public emotion in modern times. Obama struggled for words, pausing several times as he wiped away tears saying, 'This evening, Michelle and I will...hug our children a little tighter, and we'll tell them that we love them.'
Lanza is believed to have shot himself at the scene, according to the New York Times.
He was carrying three weapons including two handguns and a rifle and was wearing a bullet-proof vest, a mask and black military gear.
Three guns were found at the scene - a Glock and a Sig Sauer, both pistols - and a .223-caliber rifle.
The rifle was recovered from the back of a car at the school. The two pistols were recovered from inside the school. They were legally registered to Nancy Lanza.
A number of children were found hiding in closets in the school five hours after the shooting.
One mother told CBS that her child said there were bullets 'whizzing by' him in the hallway and that a teacher pulled him into a classroom. It was said to have been like a 'war zone'.