NEW YORK -- Mayor Michael Bloomberg stepped up his call for universal background checks for gun buyers Wednesday in the wake of the deadly Navy Yard rampage in Washington, D.C., releasing a study that he said showed thousands of felons had used federal loopholes to pursue weapons via online sales.
Bloomberg, the co-chairman of Mayors Against Illegal Guns and one of the country's most vocal proponents of stricter gun laws, said the thousands of websites offering firearms for sale were an option for felons, domestic abusers and others who would face background checks and probably be turned away if they tried to buy guns in stores.
"If it didn't work, people wouldn't do it," Bloomberg said at a news conference, where he and his chief policy advisor, John Feinblatt, released what they called the first national study of individuals with criminal records seeking to illegally acquire guns online.
The 20-page study was based on a look at selected listings posted from February to May 2013 on Armslist.com, a free site for firearms buyers and sellers to post listings. The ads studied were from would-be gun buyers, most of whom included email addresses, phone numbers or other identifying information.
Of the 607 individuals who included enough information to enable investigators to check their criminal backgrounds, 1 in 30 had committed crimes that would have blocked them from buying a gun if they had gone through a traditional firearms seller, the study said.
To ensure that matches between would-be gun buyers and criminal records were valid, investigators called the phone number posted in each ad to confirm the subscriber had placed the ad, and that the subscriber's name and date of birth matched the criminal record.
The number is a small fraction of the overall number of online ads posted annually on Armslist.com, which became active in January 2009. According to its website, Armslist.com has more than 3.5 million visits each month.
The company did not immediately respond to a request for comment.
This is not the first time Armslist.com has been singled out for criticism. The Brady Center to Prevent Gun Violence sued Armslist.com last year on behalf of the family of Jitka Vesel. The Illinois woman was shot to death in 2011 by a stalker who had bought his gun on Armslist.com.
Vesel had an order of protection against the shooter, Dmitry Smirnov, who pleaded guilty and is serving a life sentence. The lawsuit accused Armslist.com of encouraging buyers and sellers to evade laws governing gun sales, but a federal judge last month threw out the suit, which was the first to target online firearm sales.
In his decision, the judge noted that Armslist.com features a disclaimer that tells visitors to the site to "always comply with local, state, federal, and international law."
"ARMSLIST does not become involved in transactions between parties," the disclaimer adds, and it advises people to report illegal firearms activity to the federal Bureau of Alcohol, Tobacco and Firearms.
Bloomberg said that did not deter buyers with criminal records, and he called on Congress to close the online loophole by passing a law that would require a background check for every gun sale. He also said online sellers should do more to ensure that sellers and buyers on their sites are operating within the law.
According to Feinblatt, Armslist.com posts about 800,000 ads each year from buyers and sellers. It is one of thousands of websites selling weapons, Feinblatt said, quoting Justice Department figures that counted 4,000 such sites 14 years ago.
"If it was 4,000 sites 14 years ago, you can just imagine what it is today," he said.
Congress, though, has been reluctant to take on the National Rifle Assn. by toughening gun laws, even after the December 2012 Sandy Hook Elementary School shooting in Newtown, Conn., that left 20 first-graders and six school employees dead.
Monday's rampage at Washington's Navy Yard took 13 lives, including that of gunman Aaron Alexis.