But some say the shooting illustrates the need for more armed guards -- and possibly armed teachers -- in schools.
Texas Gov. Rick Perry said that if school districts decide that arming teachers is the best way to keep schools safe, so be it.
If Texas residents are duly background-checked, trained and have a concealed handgun license, "you should be able to carry your handgun anywhere in the state," Perry said, according to CNN affiliate WFAA.
Out of respect for the Newtown victims and their families, Dick's Sporting Goods has removed all guns from its store closest to Newtown, the company said.
Dick's, one of the largest sporting goods retailers in the world, also has suspended the sale of some semiautomatic rifles nationwide, the company said. It was unclear how long Dick's will keep its suspension of "modern sporting rifles."
Shedding new light on the gunman
While Carver, the chief medical examiner, said he was told that Adam Lanza had Asperger's syndrome, officials are working to determine whether that diagnosis was correct, and whether he may have had other diagnosable problems.
A former director of security for Newtown Public Schools shed new light Monday night on the gunman.
Richard Novia said Adam Lanza had Asperger's syndrome, based on documents and conversations with Lanza's mother.
Novia said that as part of his job, which he left in 2008, he would be informed of students who might pose problems to themselves or others.
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Russ Hanoman, a friend of Lanza's mother, previously told CNN that Lanza had Asperger's and that he was "very withdrawn emotionally."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.