Law enforcement officials told The Associated Press that both guns were once seized in criminal cases in Memphis. The officials described how the weapons made their separate ways from an evidence vault to gun dealers and to the shooters.
The use of guns that once were in police custody and were involved later in attacks on police officers highlights a little-known divide in gun policy in the United States: Many cities and states destroy guns gathered in criminal probes, but others sell or trade the weapons in order to get other guns or buy equipment such as bulletproof vests.
In fact, on the day of the Pentagon shooting, March 4, the Tennessee governor signed legislation revising state law on confiscated guns. Before, law enforcement agencies there had the option of destroying a gun. Under the new version, agencies may only destroy a gun if it's inoperable or unsafe.
Kentucky has a similar law, but it's not clear how many other states have laws specifically designed to promote the police sale or trade of confiscated weapons.
A nationwide review by The Associated Press in December found that over the previous two years, 24 states, mostly in the South and West, where gun-rights advocates are particularly strong, have passed 47 new laws loosening gun restrictions.
John Timoney, who led the Philadelphia and Miami police departments and served as New York's No. 2 police official, said he doesn't believe police departments should be putting more guns into the market.
"I just think it's unseemly for police departments to be selling guns that later turn up," he said, recalling that he had once been offered the chance to sell guns to raise money for the police budget.
"Obviously, we always need the money but I just said, 'No, we will take the loss and get rid of the guns,' " said the former police chief, who now works for Andrews International, a security consulting firm.
A spokeswoman for the Memphis police said gun swaps are a way to save taxpayer money.
One of the weapons in the Pentagon attack was seized by Memphis police in 2005 and traded later to a gun dealer. The gun used in the Jan. 4 courthouse shooting in Las Vegas was sold by a judge's order and the proceeds were given to the Memphis-area sheriff's office.
Neither weapon was sold by the Memphis law enforcement agencies directly to the men who used them later to shoot officers.
In both cases, the weapons first went to licensed gun dealers, but then came into the hands of men legally barred from possessing them: the Las Vegas shooter, a felon; and the mentally ill Pentagon gunman.