Toxicology tests are under way to determine whether Adam Lanza had taken medication.
Growing debate over gun laws
What happened in Newtown should never happen again, advocates on both sides of the gun-control debate agree. But they're at staunch odds about how to turn words into reality.
The National Rifle Association commented Tuesday for the first time since the shooting, saying it was shocked and heartbroken by what happened. The group is planning to hold a news conference on Friday.
"Out of respect for the families, and as a matter of common decency, we have given time for mourning, prayer and a full investigation of the facts before commenting," it said. "The NRA is prepared to offer meaningful contributions to help make sure this never happens again."
The grassroots group Newtown United sent a delegation to Washington to meet with the Brady Campaign to Prevent Gun Violence as well as families from July's movie theater massacre in Aurora, Colorado.
The new group, which formed out of Newtown on Sunday, aims to create meaningful dialogue -- both locally and beyond -- about what may have led to the tragedy.
The debate is playing out not just in Newtown and Washington, but across the United States.
Two national polls conducted shortly after the Newtown massacre suggest that more Americans want stricter gun control.
In a Washington Post/ABC News poll, 54% of adults favor stricter gun control laws in the country, while 43% oppose.
And a new CBS News poll indicates that 57% of Americans back stricter gun laws, the highest percentage in a decade; 30% think gun laws should be kept as they are.
However, less than half of the respondents in the CBS poll -- 42% -- think stricter gun laws would have helped prevent what happened at Sandy Hook Elementary.
Sen. Joe Manchin, a conservative Democrat from West Virginia and a "proud gun owner," said he's now committed to "dialogue that would bring a total change" after the massacre in Newtown.
"Who would have ever thought, in America or anywhere in the world, that children would be slaughtered?" he asked. "It's changed me."
John Licata told CNN's iReport there needs to be better vetting before people buy guns, and assault weapons should be banned -- something Sen. Dianne Feinstein, D-California, says she'll propose once the new Congress convenes in January.
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.