Hickenlooper's signature of the bills comes exactly eight months after dozens of people were shot in a movie theater in suburban Denver, the day after the executive director of the state's Corrections Department was shot and killed at his home.

Police were searching for the person who killed Tom Clements, and trying to figure out if the attack was related to his job.

The bills require background checks for private and online gun sales and ban ammunition magazines that hold more than 15 rounds.

Hickenlooper was surrounded by lawmakers who sponsored the bills at the signing ceremony. Before signing the first bill, which requires purchasers to pay fees for background checks, he looked around with a solemn look on his face and then began signing it.

Every time he signed a bill, applause erupted from lawmakers and their guests, which included families of the victims of last year's mass shootings in Aurora and Connecticut. They included Jane Dougherty, whose sister was killed in a deadly attack at Sandy Hook Elementary in Newtown, Conn., and Sandy Phillips, whose daughter was killed in theater shooting in Aurora.

Phillips, who lost her daughter Jessica Ghawi, reminded Hickenlooper that it was the eight month anniversary of the rampage.

"You've given us a real gift today," she told the governor.

Later, Phillips added: "Thank you so much. You're leading the entire country."

Dougherty also went up to Hickenlooper to thank him with tears in her eyes. After signing the bills, Hickenlooper hugged various lawmakers and victims.

The bills thrust Colorado into the national spotlight as a potential test of how far the country might be willing to go on new restrictions after the horror of the Newtown and Aurora shootings.

"I am happy the governor is signing common-sense legislation that reduces gun violence in our communities by keeping guns out of the hands of criminals, domestic violence offenders and the seriously mentally ill," said Democratic Rep. Rhonda Fields, who represents the district where an assailant opened fire July 20 during a midnight showing of "Dark Knight Rises."

The shootings led Hickenlooper and other state Democrats to take on gun control, and they have succeeded where their party has not in most other states.

This month, Washington State's Democrat-controlled House couldn't advance a universal background check bill. A bill requiring background checks at gun shows in New Mexico also failed in the Democrat-led Legislature.

The bills getting Hickenlooper's signature are centerpieces of a package of Democratic gun bills introduced this session. With his signature, gun sales and transfers between private parties and purchases conducted online will be subjected to background checks. Ammunition magazines that hold more than 15 rounds will be banned and subject to criminal penalties. Both bills take effect July 1.

Lawmakers debated firearms proposals after the Columbine High School shootings in Colorado in 1999, and began requiring background checks for buyers at gun shows. But nothing they did then was as sweeping as the proposals they took up this year.

Republicans have warned that voters will punish Hickenlooper and other Democrats who voted in favor of the measures.

"I'm telling you, they have overreached, and there are going to be electoral consequences," said Republican Sen. Greg Brophy.

A Colorado-based manufacturer of magazines plans to relocate because of the new restrictions. Republicans have bashed Democrats, saying their proposal to limit magazine sizes will drive jobs from the state, and ultimately won't prevent criminals from getting larger magazines in other states.

Some county sheriffs also opposed the new background checks, arguing they're unenforceable and endanger people's Second Amendment rights. Two ballot measures have already been proposed to try to undo the gun restrictions.