From the time he was little, Adam Lanza couldn't bear to be touched. By middle school, the chaos and noise of large, bustling classrooms began to upset him. At 20, just before the Newtown shootings, he was isolated and, the world would later learn, disturbed.
All this was revealed in "Raising Adam Lanza," an investigative report by the Hartford Courant in partnership with the PBS news program FRONTLINE, which aired Tuesday night.
Before the age of 6, Lanza had been diagnosed with a controversial condition, "sensory integration disorder" -- now known as sensory processing disorder, according to the report.
Those with sensory processing disorder or SPD may over-respond to stimuli and find clothing, physical contact, light, sound or food unbearable. They may also under-respond and feel little or no reaction to pain or extreme hot and cold. A third form involves sensory motor problems that can cause weakness and clumsiness or delay in developing motor skills.
Whether SPD is a distinct disorder or a collection of symptoms pointing to other neurological deficits, most often anxiety or attention-deficit hyperactivity disorder (ADHD), has been debated by the medical community for more than two decades.
No one will know why the withdrawn Lanza shot his mother four times in her own bed, then went to Sandy Hook Elementary School to slaughter six women and 20 first-graders before taking his own life on Dec. 14, 2012.
But this report, the most detailed account to date on his troubled life, paints a picture of a child coping with special needs and a mother, "devoted but perhaps misguided," struggling unsuccessfully to help.
"The most surprising thing for me was this sort of inwardness of Adam, a world view of someone that was afraid of the world," said show producer Frank Koughan. "He just reacted badly to the whole world and didn't want to be part of it. He was not some violent monster, except on one particular day, when he was exceedingly monstrous."
The investigative team interviewed family and friends of the shooter's parents, Nancy and Peter Lanza, and reviewed a decade's worth of messages and emails from his mother to close friends, describing her son's socially awkward behavior.
"Adam was a quiet kid. He never said a word," Marvin LaFontaine, a friend of Nancy Lanza, told them. "There was a weirdness about him and Nancy warned me once at one of the Scout meetings … 'Don't touch Adam.' She said he just can't stand that. He'd become teary-eyed and I think he would run to his mother."
In 1998, the Lanzas left their home in New Hampshire for Connecticut with Adam, who had already been diagnosed with the sensory disorder and was "coded" with an individual education plan, according to a family member who did not want to be identified by FRONTLINE.
"It was somebody well-placed who was completely in a position to know," said Koughan, 45, a veteran journalist who produced the film, "Drop-Out Nation."
Lanza didn't recognize pain, another feature of some types of SPD. He couldn't cope with loud noise, confusion or change, which would cause him to "shut down," according to the report.
"He'd almost go into a catatonic kind of state, which is another reason why in hindsight, he didn't seem like a threat to anybody," said Koughan. "He didn't lash out or beat up kids. He went within himself, until one day he didn't."
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.
A psychologist mom who did not want her name used, was referred to Miller by her son's occupational therapist. As a baby, her son Michael cried constantly and was difficult to soothe, requiring endless swaddling and lots of movement. Eating seemed to over-stimulate him and he gagged on his food.
"You could never get him swaddled tight enough or push the stroller fast enough," she said. "He would kind of look over my eyes, instead of looking into my eyes."
Michael, not his real name to protect his privacy, was slow learning to talk, and when he did, he used advanced language -- words like "obsolete."
His mother feared her son had Asperger's syndrome. "He spoke in complete sentences really beautifully," the mom said. "He did have this weird intonation with question marks – 'Mommy?' and 'Look over here?' … He wasn't giving eye contact or saying, 'Mommy, I love you."
As a 4-year-old in preschool, he couldn't sit still at circle time, so he stood on his head at the back of the classroom in order to concentrate and answer the teacher's questions. "Everything else became overwhelming," said his mother.
In therapy, which was not covered by insurance because it is not a recognized disorder, the family was taught to "shift to his world" rather than force him to adapt.
The results at the STAR center were "transformational," said the mom. His language "took off" and today, at 8, he is on a swim team. Though Michael knows his body is "different," he seems to be "growing out" of the SPD, she said.
Family stress and anxiety results when children are untreated, according to STAR's Miller. Like Michael and perhaps Adam Lanza, they are often teased "unmercifully" and misunderstood. She said families dealing with SPD have "significantly more stress" than children diagnosed even with bipolar or other psychiatric disorders.
"If the environment is attacking you, you would be nervous, too," she said. Parents like Nancy Lanza need support, and their children need friends, said Miller.
"Anyone who is a loner needs support," said Miller. "That's part of the story here. We need to take a look not just at gun control, but what we can do to reach these children."
Like other professionals, Miller said linking SPD to violence is "absolutely the wrong message to a parent."
"That's such a complicated pathway, and it's multifactoral," she said of what leads a child to be a killer. "But [Adam Lanza] likely didn't get the support.. … Parents are left on their own to defend their children."
The Courant/FRONTLINE report cited other factors that influenced Adam Lanza. His mother took him out of high school his sophomore year and he lost his peer support and special needs psychologist and became more isolated. Police found thousands of dollars worth of violent video games in the family home.
Lanza's parents separated in 2001 and divorced in 2009. He eventually became estranged from his father, Peter Lanza and brother Ryan. His mother, who loved to travel, was spending more time away from their home to foster her son's independence.
He dropped out of Western Connecticut State University where he had taken some classes.
"At one point in 2009 or 2010, he goes off the grid," said producer Koughan. "He is no longer in school and he is staying at home, rarely venturing out of the house. That's where the black hole of information goes. Nancy is not having friends over to the house and no one really sees him until Dec. 14. What happened during that period, we really don't know."
The investigative team was never able to find any reason why Adam Lanza chose Sandy Hook Elementary School to unload three of his mother's firearms on innocent children and then himself.
"There was no indication there was traumatic episode there," said Koughan, who unearthed a photo from Lanza's first-grade class. "He's got a smile that looks more like a grimace -- that could just be a bad photo. But he looked uncomfortable among his classmates."