Lt Paul Vance from Connecticut state police said they had seized a "significant" amount of evidence from Adam Lanza's home.
He added that there were no previous concerns over Lanza.
A list of the victims from the US school shooting has been published. Twenty students and six teachers were killed in the massacre.
The most disturbing feature of the rampage is what we do not know. We still have no idea why Adam Lanza acted with this cowardly savagery.
There are reports claiming that Adam Lanza went to the school a day before the massacre. They say he had a major confrontation with staff.