Andrew C. Thomas, who killed himself after shooting Fox, got his gun through a straw purchaser - one who legally buys guns for a felon barred by law from owning firearms. Thomas was a convicted felon.
The law, effective Dec. 26, restores a minimum five-year prison sentence for those convicted of repeat straw purchases.
"Officer Fox died in the line of duty last year at the hands of a felon who should never have had a gun and, less directly, by the hand of the man who later admitted buying the gun and passing it along," Corbett said.
The governor spoke at a lectern with Fox's police cruiser behind him. The car has been taken out of regular use and has a black cloth covering its rooftop lights.
Corbett said he hoped the tougher penalty would discourage people from buying firearms for felons. It was a sentiment shared by Fox's family, colleagues, officials, and police from throughout Montgomery County and the region.
The ceremony - and the law - meant a lot to Plymouth Township Police Department members.
"He was our brother," said Deputy Chief John Myrsiades, "but so are all of the other police officers, and this law is something that, hopefully, makes our job safer and the community safer."
The event took place amid a broader debate on gun violence following the December shootings at a Newtown, Conn., school that killed 20 children and six adults.
Vice President Biden on Thursday said that his working group on gun violence, created after the Sandy Hook Elementary School shootings, probably would recommend universal background checks for gun buyers and a ban on high-capacity ammunition magazines. The statement came after Biden's group met with representatives from various sporting and gun-rights organizations, including the National Rifle Association.
The NRA quickly criticized Biden's comment, saying the Obama administration was "pushing failed solutions to our nation's most pressing problems. We will not allow law-abiding gun owners to be blamed for the acts of criminals and madmen."
Corbett was reluctant to talk about gun policy politics after the signing: "We're here today on something that, while it's very related to guns, is not related to Sandy Hook."
The governor, an NRA member, said current laws need to be enforced. His administration will wait to study actual recommendations, he said, rather than react to early statements that are "more positioning than anything else."
Tom Fox, father of the slain officer, said he does not think law-abiding citizens need to have their firearms taken away, but he does not want guns in the hands of criminals, either. An assault gun ban, which also has been discussed in Washington, would be "a start," he said. "I don't see a purpose to assault guns."
In gun debate, video game industry defends itself. A4.
Wynnefield resident hit by gunfire while he was sleeping. B2.
Contact Carolyn Davis at 610-313-8109, email@example.com, or @carolyntweets on Twitter.