"It is currently estimated that the time from when theshooter shot his way into theschool until he took his own life was less than five minutes, " Sedensky wrote.
The informant also said that theshooter "had attended Sandy Hook Elementary School and that theschool was Adam Lanza's 'life, ' " according to the documents.
After gunfire at theschool killed 20 children and six adults -- the second deadliest school shooting in U.S. history -- theshooter killed himself, officials said.