Go inside the investigation into one of the worst school shooting massacres in U.S. history.
No clear motive was spelled out in the 44-page summary of the investigation into last year's massacre at Sandy Hook Elementary School that was released Monday. However, new photographs of the scene -- and shooter Adam Lanza's home -- were released. Here is a sampling:
Enrique Castro-Mendivil / Reuters
U.S. National Archives
REUTERS/ Stefano Rellandini
U.S. Air Force
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