He also said he received "intake information," which he said "is common for any students troubled or impaired or with disabilities." The idea was to keep track of and help students who may need it.

However, Novia said he never thought Lanza was a threat and certainly never thought he was capable of such violence.

Russ Hanoman, a friend of Lanza's mother, previously told CNN that Lanza had Asperger's and that he was "very withdrawn emotionally."

CNN has not been able to independently confirm whether Lanza was diagnosed with autism or Asperger's, a higher-functioning form of autism. Both are developmental disorders, not mental illnesses.

Many experts say neither Asperger's syndrome nor autism can be blamed for the rampage.

"There is absolutely no evidence or any reliable research that suggests a linkage between autism and planned violence," the Autism Society said in a statement. "To imply or suggest that some linkage exists is wrong and is harmful to more than 1.5 million law-abiding, nonviolent and wonderful individuals who live with autism each day."

Dr. Max Wiznitzer, a pediatric neurologist and autism expert at Rainbow Babies and Children's Hospital in Cleveland, also said the gunman's actions can't be linked to autism spectrum disorders.

"Aggression and violence in the ASD population is reactive, not preplanned and deliberate," he said.