After the assassinations of Martin Luther King and Robert Kennedy in 1968, Congress made it difficult for people convicted of felonies to obtain a weapon, even after serving their sentence. But in the past decade, under pressure from gun rights groups, individual states have loosened restrictions. Currently, laws vary state by state. In some cases, individuals who have served their sentence automatically get their gun rights restored; in others it takes action by the governor.

"This is a patchwork nation," said Margaret Love, an attorney in Washington, D.C., specializing in restoration of civil rights by convicted felons. "In some states is relatively easy to get federal and state rights back, others where it’s almost impossible."

What concerns gun control advocates are the loopholes in many state laws. A New York Times investigation in 2011 found thousands of people convicted of violent crimes getting their guns back with little effort, including people who have gone on to commit murders with these weapons.

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"It’s part of the trend in the states under pressure from lobbying groups to relax restrictions across the board, whether its concealed carry or restoration," said Richard Painter, a law professor at the University of Minnesota. "It fits into that larger picture."

In 1986, Congress amended the federal firearms law to allow exemptions to the earlier broad ban of gun ownership for felons. It allowed people to get their rights restored with a pardon, expungement or other action taken by a state court. Since then, states have taken different tacks when it comes to restoration, according to Love.

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In North Dakota, for example, people convicted of a felony never actually lose their gun rights. In Colorado, it takes a governor’s pardon, which is seldom granted. However in Nebraska, Nevada, Connecticut and Georgia, getting a pardon for restoration is much more common. In many states, local prosecutors don’t have to be notified that the convicted felons are trying to regain their guns -- a procedure that could safeguard violent offenders from regaining weapons. (Chart: See state-by-state requirements for gun rights restoration.)

While banning convicted felons from owning guns may appear to be good policy, Painter says it may not be the most effective way to ensure public safety. He notes that felonies cover everything from tax cheaters to shoplifters and mass murderers.

"Denying gun rights to convicted felons sounds like a good idea. It’s a very rough measure of risk, depending on the type of felony," he said. "My concern over denying gun rights of felons is we don’t address the large number of high-risk people who have not been convicted of felonies who should not have guns in the house."