Evidence has been found that could help explain the motives of the lone gunman behind one of the worst mass school shootings in American history, police said on Saturday.
Officers found evidence at Sandy Hook Elementary School in Newtown, Connecticut, where 20 children and six adults were shot and killed, and at a second crime scene where a woman was found dead, Lt Paul Vance told a press conference.
The gunman is believed to be 20-year-old Adam Lanza, who killed his mother Nancy at their home before going on the rampage at the school, although Lt Vance refused to confirm the gunman's identity.
"Our investigators at the crime scene, the school and secondarily at the secondary crime scene we discussed where the female 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 said.
He also revealed the gunman forced his way into the school.
Lt Vance added: "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."
Lanza shot dead 18 children aged between five and 10 and six adults at the school where his mother Nancy was a teacher, before killing himself.
Two other children shot at the scene died in hospital later.
Lt Vance said that the identity of those killed had been confirmed and that they would be released as soon as possible.
Those believed dead include principal Dawn Hochsprung, who had been in charge since 2010.