But a national autism committee cautioned against speculating about any link between autism and violence.
"Some public comments have drawn potentially inaccurate and stigmatizing conclusions about a link between the diagnosis and a propensity for violence and lack of empathy," according to a statement from the Autism Research Institute's Autistic Global Initiative Project.
"Autism is not a mental health disorder - it is a neurodevelopmental disorder. ... The eyes of the world are on this wrenching tragedy -- with 1 in 88 now diagnosed, misinformation could easily trigger increased prejudice and misunderstanding."
A former classmate told CNN affiliate WCBS that Lanza "was just a kid" -- not a troublemaker, not anti-social, not suggesting in any way that he could erupt like this.
"I don't know who would do anything like this," the classmate said, before walking away distraught. "This is unspeakable."
The suspect's father was also at a loss for explanation. He sent his condolences to the families of victims in a statement released Saturday.
"Our family is grieving along with all those who have been affected by this enormous tragedy," he said. "No words can truly express how heartbroken we are. We are in a state of disbelief and trying to find whatever answers we can."