WASHINGTON — Sen. Mark Pryor, D-Ark., introduced legislation Wednesday intended to better identify prospective gun buyers deemed mentally unfit to own them.

The bill would clarify circumstances under which a person would be added to the National Instant Criminal Background Check System based on mental illness.

The system, which serves as a clearinghouse for licensed gun dealers, should be strengthened as part of any federal effort to address the December mass shooting of school children in Connecticut, Pryor said.

"One of the things I keep hearing is, let’s enforce the laws we have on the books," Pryor said. "This (bill) will keep guns out of the hands of people who shouldn’t have guns."

Pryor joined Sens. Lindsey Graham, R-S.C., Mark Begich, D-Alaska, and Jeff Flake, R-Ariz., at a news conference in the Capitol to unveil the legislation.

Graham launched the effort last month after a woman in Columbia, S.C., was arrested for attempting to shoot a gun inside a local school.

Three days earlier, the woman passed the federal background check and purchased the gun even though a 2005 federal indictment accused her of threatening to kill President George W. Bush and members of Congress. She had pleaded innocent by reason of insanity in 2009.

"This is one area we ought to be able to rally around," Graham said Wednesday.

Added to the NICS database under the bill would be those that a federal court has determined are an imminent danger to themselves or others, those found not guilty by reason of insanity and those who required involuntary inpatient or outpatient treatment by a psychiatric hospital.

The legislation also provides a mechanism for removing from the list individuals who have recovered from their mental illness.