UNDATED (CNN) -- A PBS documentary provides new details about Adam Lanza, the gunman in the Sandy Hook Elementary shooting.
In "Raising Adam Lanza," people close to the family talk about their impressions of Lanza.
The writer and producer told CNN Wednesday what they were able to learn from the film. Frank Koughan says, "I think the thing that we learned most about him is how strange a child he was and how though he committed a truly monstrous act, there was nothing monstrous about him growing up. He was, if anything, exactly the opposite. He was very meek, fearful of the world, very easily spooked by things that you and I would find completely unremarkable. And it doesn't jive with somebody who then walks into an elementary school and starts spraying gunfire all over the place. So something happened late in his life that caused a drastic snap. And what that is, is the question that's still unanswered."
A source close to the investigation tells CNN Lanza was obsessed with other mass murders.
Police say Lanza took his own life in December after killing his mother and 26 people, including 20 children.