A documentary about Newton, Conn., mass shooter Adam Lanza will air Tuesday night on PBS and reveal new details about the teenager, including a recount of the years leading up to Dec. 14, 2012, when he killed 26 children and women.

A Hartford Courant/Frontline investigation found that Lanza spent much time alone in the months leading up to the mass shooting at Sandy Hook Elementary School, with his mother, Nancy Lanza, encouraging him to be independent despite his metal disabilities, according to Yahoo!

Reports from the investigation will be included in the documentary entitled Raising Adam Lanza.

On Dec. 14, Adam, 20, shot and killed his mother Nancy in the home they shared before making his way to the elementary school and killing 20 children and six women. He then committed suicide.

Adam's began to withdraw socially after he left Newtown High School at the age of 16 to enroll in a nearby college, Courant reporters Alaine Griffin and Josh Kovner found. He dropped out of college and had not attended school since 2010. Between 2010 and 2012, Nancy took her son to practice at gun ranges to practice shooting, which friends said was a way for the mother and son to bond. She also purchased four firearms during the same time period.

"We had heard so much about her being this paranoid, doomsday prepper who was stockpiling food and waiting for this economic collapse,'' Griffin said. "We learned through our reporting that she had done a number of things to get Adam in the right place - all these different educational shifts in and out of school. We learned that she was trying to do the right thing by Adam. Whether or not it was remains to be seen."

Additionald details discussed in the documentary include the thousands of dollars worth of violent video games found in the Lanzas' home and how Adam might have felt like he was in competition with mass murderer Anders Breivik, based on articles about the Norwegian's crimes that police found in the Lanzas' home.

At a young age Adam was diagnosed with sensory integration disorder and then with Asperger's when in middle school. Both conditions combined result in a person being socially challenged and having trouble dealing with extreme effects to the senses such as bright lights and loud noises.

Nancy and her husband officially divorced in 2009, though they had been separated since 2001. Adam has one brother and reportedly cut off contract with his father following the divorce.

"I think he did what he knew how to do,'' Griffin said. "Graphically, violent video games don't make you turn to violence if that's not your predisposition, but this kid had a lot going on and when it came time for him to carry out this terrible rampage, he did it in a way he was accustomed to.''

PBS' Frontline with Hartford Courant will air Raising Adam Lanza on Tuesday at 10 p.m.