— A lone police cruiser outside Columbine High School was the only outward reaction Friday to an even deadlier attack at a Connecticut elementary school.

But in a state that was rocked by the 1999 Columbine school massacre and the Aurora movie theater shooting less than six months ago, Friday's shootings renewed debate over why mass shootings keep occurring and whether gun control can stop them.

"Until we get our acts together and stop making these ... weapons available, this is going to keep happening," said an angry Tom Teves, whose son Alex was killed in the theater shooting last July in the Denver suburb of Aurora.

Teves was choked up as he answered a reporter's call Friday. A work associate of his lives in Newtown, Conn., where 27 people were killed, including 18 children, at Sandy Hook Elementary. The connection chilled and angered him.

The Connecticut gunman was reported to have used a .223-caliber rifle, although it wasn't immediately clear what type. Weapons that use the .223 caliber ammunition can range from assault-style rifles similar to the AR-15 semi-automatic used by James Holmes in Aurora in the July 20 shooting that killed 12 people and wounded 70 to hunting rifles.

The gunman in the recent Oregon shopping mall shooting also used an AR-15, and the Washington, D.C.-area snipers John Allen Muhammad and Lee Boyd Malvo used a .223-caliber Bushmaster, both largely civilian versions of the military's M-16.

Versions of the AR-15 once were outlawed under a U.S. assault weapon ban in 1994. That prohibition expired in 2004 and Congress, in a nod to the political clout of gun enthusiasts, did not renew it.

This week, Colorado Gov. John Hickenlooper generated a storm of debate after declaring that it was time to start debating gun control measures. Hickenlooper specifically mentioned the AR-15.

"When you look at what happened in Aurora, a great deal of that damage was from the large magazine on the AR-15. I think we need to have that discussion and say, 'Where is this appropriate?'" Hickenlooper said Wednesday.

After Friday's school shootings, Hickenlooper wrote on Twitter, "We know too well what impact this kind of violence has on a community and our nation."

A visibly emotional President Obama seemed willing to renew debate, calling for "meaningful action" to prevent similar shootings.

Also Friday, Mark Kelly, the astronaut husband of former U.S. Rep. Gabrielle Giffords, who was shot in the head during an attack that killed six people in Tucson, Ariz., last year, said the Connecticut shooting should "sound a call for our leaders to stand up and do what is right."

"This time our response must consist of more than regret, sorrow, and condolence," Kelly said on his Facebook page, calling for "a meaningful discussion about our gun laws and how they can be reformed and better enforced to prevent gun violence and death in America."

Tom Sullivan, whose son Alex also died in the Aurora theater shooting, welcomed the discussion.

"Clips that hold 50 bullets? The only animal you're after with that is man. There is no other reason. That's what that is used for. My question to those people is, 'Why do you need a clip that holds 50 bullets?'" Sullivan said in a phone interview.

But Sullivan said mental health, not gun control, is a more pressing concern.

"We all need someone in our lives to care," Sullivan said. "If we see a friend, a colleague, a co-worker and they're having a hard time, we need to reach out."

No amount of discussion eases the pain, Colorado shooting survivors said.

"It's so sad. It's just so sad," said Judy Brown, whose son, Brooks, was threatened by one of the Columbine killers, Eric Harris, about a year before the shootings there. The family tried to alert authorities that Harris was dangerous.

Judy Brown said she hopes friends of the Connecticut shootings will comfort them over the long run, not just in the initial weeks and months.

"Send them calls. Call them on the phone. Leave them messages. Let them know that you haven't forgotten. It doesn't go away. It's a lifetime struggle.

"It never, ever, ever, goes away. It never goes away," she said, and began to weep.

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Associated Press writers Brian Skoloff in Phoenix and P. Solomon Banda, Dan Elliott and Kristen Wyatt in Denver contributed to this report.