An astounding assortment of ammunition and weapons, including rifles, knives and samurai swords; damaged computer equipment; journals and a newspaper clip of a school shooting at Northern Illinois University.

Those were among a chilling inventory of items the police found in the home where Adam Lanza plotted one of the deadliest school shootings in the nation’s history, according to search warrants of the home unsealed for the first time since the Newtown massacre in December.

Mr. Lanza, 20, killed his mother, Nancy Lanza, on Dec. 14 in the spacious yellow home they shared in Newtown. He then drove to Sandy Hook Elementary School, which he attended as a child, and killed 20 first graders and 6 educators before killing himself as police officers arrived.