HARTFORD, Conn. (AP) — A yearlong investigation into the Newtown school shooting has provided disturbing insights into the 20-year-old gunman, but it still has not provided a motive.

Prosecutors closed the case Monday on the Sandy Hook Elementary shooting. Their report offers a chilling portrait of gunman Adam Lanza as a loner who was obsessed with violence. But they were unable to answer the question that everyone has been asking: Why?

State's Attorney Stephen Sedensky III says there is no clear indication why Lanza chose Sandy Hook Elementary other than that it was close to his home.

Lanza killed 20 first-graders and six educators with a semi-automatic rifle on Dec. 14. He also shot his mother in the forehead inside their home. He committed suicide with a handgun as police arrived at the school.

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