Honking car horns from an anti-gun control rally outside the Capitol in Denver were a persistent backdrop to the proceedings, in which the Senate considered a measure that passed the House in February, 36-29, The Denver Post reported.
Among those testifying in favor of the measure was Mark Kelly, the husband of former U.S. Rep. Gabrielle Giffords, D-Ariz., who was critically injured in a mass shooting in 2011.
"We're both gun owners," Kelly said of himself and his wife, "but we're anti-gun violence, and this bill will prevent violence."
The legislation is intended to close a loophole in gun sales, requiring background checks on the transfer of all guns in the state. Current state law requires purchasers of guns from retail dealers to undergo a background check administered by the Colorado Bureau of investigation, but exempts private sales and transfers of guns between individuals, the newspaper said.
Sponsor of the bill, state Sen. Morgan Carroll of Aurora said the theater shooting in her district prompted her support of the bill.
"It's personal to me that this become law," she said.
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