"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 thanked Hickenlooper with tears in her eyes. Mauser also expressed gratitude.
"I knew it would be a long haul," he said. "But I had faith in the people of Colorado."
Democratic Rep. Rhonda Fields, who represents the district that includes the Aurora theater, said the governor had signed "common-sense legislation."
"Gun violence is a problem nationwide, and sadly in the state of Colorado, we are all too familiar with some of these tragedies," Fields.
Lawmakers debated firearms proposals after the Columbine High School shooting, 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.
This year, Colorado lawmakers succeeded while members of their party stumbled in other states.
Washington state's Democrat-controlled House failed this month to pass a universal background check bill. A bill requiring background checks at gun shows in New Mexico also stalled in that Democrat-led Legislature.
Republicans have warned that voters will punish Hickenlooper and other Democrats who voted in favor of the measures.
"The real solution here is at the ballot box in 2014," Brophy said.
Republicans have said limiting magazine sizes will drive jobs from the state, and ultimately won't prevent criminals from getting larger magazines in other states.
One Colorado-based manufacturer of ammunition magazines disclosed plans to relocate because of the new restrictions.
Police chiefs in urban areas supported the bills, but some rural county sheriffs opposed the new background checks, arguing the move is unenforceable and endangers Second Amendment rights.
Hickenlooper said law enforcement should try to find common ground.
"This shouldn't be rural versus urban. We are one state," he said.
Associated Press writer Kristen Wyatt contributed to this report.
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