In middle school, according to an interview with Richard Novia, who served as security chief for Newtown schools and advised the tech club, Lanza was diagnosed with Asperger's syndrome, a part of the autism spectrum. Novia told Nancy Lanza, he worried about the boy being bullied.
Asperger's can be linked to or confused with SPD, but neither condition is associated with violence, mental health experts tell ABCNews.com. But they suggest the complexity of anxiety and alienation in a child could shed light on other factors that may have set Lanza up for a breakdown.
"What it sounds like to me is you have a kid who probably had what has been described really well as social anxiety," said Dr. Max Wiznitzer, a pediatric neurologist who specializes in development and behavioral disorders, including autism, at UH Rainbow Babies & Children's Hospital in Cleveland, Ohio.
"These behaviors [described by the FRONTLINE report] could have set him up for being bullied and somewhat ostracized and made fun of by his peers," he said. "With a certain type personality, he could ruminate on it and get stuck. Maybe he got angry and took the wrong road. But why did he not go after his peers, not little kids?"
As for Asperger's syndrome, Wiznitzer said of Lanza, "There is insufficient data … We don't know who diagnosed him."
Sensory processing disorder is a controversial condition. Just this year, its submission to the American Psychiatric Association for inclusion in the 2013 Diagnostic and Standards Manual (DSM V) was rejected.
Wiznitzer says there are no distinct criteria for diagnosing SPD and that it masks other distinct conditions like anxiety, obsessive compulsive disorder (OCD) and attention-deficit hyperactivity disorder (ADHD), which can be treated with conventional drugs or cognitive therapy.
As for Lanza, he said, "You have no idea what it was like at home -- a person with extreme anxiety keeps very quiet in the outside world. Sometimes with anxiety-based behavior -- and I am not saying he had this -- if he had a change in how he was functioning, it could lead to a thought disorder."
The concept of SPD was developed by California psychologist A. Jean Ayres, who wrote a 1972 book that argued sensory problems were part of a distinct brain disorder. Today, the leading advocate for its inclusion in the DSM V is Lucy Jane Miller, an occupational therapist who founded the Colorado-based Sensory Therapies and Research (STAR) Center for treatment of children and adults.
The center offers sensory-based services for clients and their families living with SPD and other attention deficit, anxiety and autistic spectrum disorders. Through desensitization therapies, they help children learn to play with friends, enjoy school and complete daily routines. Their services help adults to understand and to cope with how sensory issues affect their quality of life. SPD acts like a neurological "traffic jam," and those with the condition "misinterpret" touch, sound or movement, according to Miller.
"An over-responsive child like Adam Lanza won't let people touch them, and if they are touched by accident in a line at school, they will turn around and hit someone," she told ABCNews.com. "It's a fight or flight response caused by the nervous system."
"The fire engine goes by and they clasp their hands on their ears," said Miller. "Some hear whispers in the classroom and say it sounds like 'a war going on in the school.' "
Some children cannot take a test because the sound of scratching pencils on paper is intolerable. Those over-responses "looks like anxiety or OCD," she said.
Other "crave" sensory input, hugging and grabbing at people and are often expelled from pre-school, told they have attention deficit hyperactivity disorder.
Miller argues that the medical community has limited research for a disorder they don't understand. Before autism had a label, mothers were blamed for their children's unresponsiveness, called "refrigerator mothers," she said.
The problem with their argument, is that anxiety and other disorders are "defined by behaviors," said Miller. "None of them are defined by biological markers."
"The truth is we need more research," she said. "Our program at the STAR Center sees 400 families a year. Many of these children have significant feeding and sleeping problems as infants and are very disregulated before anxiety disorder would develop. You don't think about eating when you are three months old."
STAR's program is based in parent education and intensive coaching. "We are getting them so they have typical relationships with their parents and so their parents can love them again," said Miller.