The gunman, 20-year-old Adam Lanza, used a high-powered riffle and had an arsenal of hundreds of rounds of especially deadly ammunition, reports have stated. He killed himself about 10 minutes after starting the attack.

The Associated Press reported that Lanza is believed to have used a Bushmaster AR-15 rifle in the school attack, a civilian version of the military's M-16. Some AR-15s were outlawed as part of the 1994 assault weapons ban. But that law expired in 2004, and Congress did not renew it after heavy pressure from gun-rights lobbyists.

Democrats have called for reinstating the assault weapons ban among other gun-control measures when Congress returns next year.

“We can’t just say people are violent and turn away,” Lieberman said. “We have the power to do something about this. … We can save a lot more than one child if we work together on this.”

Blumenthal had to pause a moment, almost overtaken by emotion, when he recounted going to the Newtown firehouse last Friday, where parents found out whether their children were among those killed.

“I will live forever with the sights and sounds of those parents as they emerged from the firehouse,” Blumenthal said. “Newtown is a call for national reflection. … It’s also a call for action.”