Accused Newtown shooter Adam Lanza was spending more time alone in the months leading up to the mass shooting as his mother, Nancy Lanza, attempted to encourage him to be independent despite his mental disabilities, a Hartford Courant/Frontline investigation has found. In a new documentary called "Raising Adam Lanza," which airs Tuesday night on PBS, reporters from the Courant attempt to retrace the steps taken by Nancy and Adam in the years leading up to the shooting, complicating the picture that has occasionally appeared in the media of Nancy as a gun obsessed mother who was in denial about her son's mental challenges.

Adam is believed to have shot his mother four times in the head as she slept on Dec. 14 before shooting his way into Sandy Hook Elementary, where he attended school as a child, and killing 20 children and six women. He then took his own life.

Frontline and The Hartford Courant provided Yahoo News with several previously unpublished childhood and teenage photos of Adam Lanza they uncovered in their investigation.

The 20-year-old had been spending more time alone in his mother's $500,000 home in the affluent Connecticut suburb in the months leading up the shooting, Courant reporters Alaine Griffin and Josh Kovner found. Adam's social world gradually began shrinking after he left Newtown High School at the age of 16 to enroll in a nearby college, where he made As and Bs before withdrawing there, as well. Since 2010, Adam had not attended school.

Between 2010 and 2012, Nancy took Adam to nearby gun ranges to practice shooting. Nancy purchased four firearms, including the Bushmaster semi-automatic rifle Adam is believed to have used in the attack, during the same period. Her friends say Nancy used target practice as a way to bond with her withdrawn son. Police also uncovered thousands of dollars worth of violent video games in the Lanzas' home. Police believe Adam may have been inspired by the video games he played in the attack, since he changed the magazines of his weapons more frequently than was necessary, Frontline reported. Late Sunday, the Courant also reported that Adam may have felt that he was in direct competition with Norwegian mass murderer Anders Breivik, based on news articles about Breivik's 2011 crime they found in the Lanzas' home.

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In the months before the attack, Nancy took frequent trips and left Adam at home unsupervised--including on one trip this past Thanksgiving--in an attempt to make him more independent.

Her friends say Nancy is the forgotten 27th victim that day.

"She's been described as some sort of gun nut or survivalist and this other misconception that she was a bad mother," her friend John Bergquist told Frontline. But he said her life "revolved around caring for Adam."

Adam was diagnosed at a young age with sensory integration disorder, a medically controversial diagnosis that meant Adam had trouble coping with bright lights, loud noises, and knowing when he was in pain. Later, when he was in middle school, Adam was also diagnosed with Asperger's, a condition related to autism that can make social interaction challenging. (Medical experts cautioned that autism disorders are not associated with violent behavior.)

A friend of Nancy’s remembered that when Adam was just six years old, he did not like to be touched. If children his age touched them, he recoiled or became upset. "He was angry with them," Marvin LaFontaine, Nancy's friend, told Frontline. Richard Novia, who co-founded the tech club Adam joined while he attended Newtown High School, told Frontline Adam would have "episodes" as a teen where he would completely withdraw from the world, sometimes sitting in a corner, motionless.

Nancy raised Adam and his older brother in their Newtown home on her own after she and her husband separated in 2001. In 2009, the couple officially divorced, and Adam abruptly cut off contact with his father in 2010 for reasons that are unclear.

Nancy's friends said she was planning on moving to either Washington or North Carolina to enroll Adam in college again, so that he could get a degree in history.

