Overall, according to the group, nine of 13 sales in the sting operation in Utah would be considered illegal transactions because the investigator posing as a buyer admitted he couldn't pass a background check.
New York Mayor Michael Bloomberg, who is co-chairman of the 550-member mayors group, said it's a giant loophole for felons to acquire guns.
"Websites are becoming the new gun shows," Bloomberg said in the group's statement. "Most gun sales are perfectly legal, including sales on the Internet. But until the background check law covers all gun sales, these websites will continue to be used by criminals to slip through the gaps."
Private, one-on-one sales of guns are legal in Utah the only restriction is a federal law requiring the seller to make sure the purchaser is of legal age to buy a gun, lives in the same state and isn't planning to commit a crime with the weapon. Saying you can't pass a background check could make the sale illegal.
It's a less stringent requirement than what licensed gun sellers must do, including background checks and a follow-up call by the dealer to the Utah Bureau of Criminal Information on the criminal background check.
On the audio of the Orem sale, the anonymous investigator says to the unnamed seller, "No background checks?"
The seller responds, "No background checks," and the investigator posing as a buyer responds by saying, "That's good 'cause I probably couldn't pass one."
The seller laughs and then says, "Yeah, if you're gonna use it on somebody afterwards, I might have to use my other gun on your ass."
The push by the Mayors Against Illegal Guns none of whom are based in Utah also once again cast a light on KSL.com's sizable classified listings for guns.
On Thursday, there were more than 6,400 listings under the "Firearms and Hunting" section on the website with 1,536 being handguns and 1,078 under the label of rifles.
In May, Russell Banz, vice president of products for Deseret Digital Media, said the company was seeking input from the community and guns-rights advocates after it ran an online survey about whether it should ban gun listings.
At the time, in an interview with The Salt Lake Tribune, Banz said a decision would be made on whether to continue the gun listings.
An email to Banz and a message left with Deseret Digital Media on Thursday weren't returned.
Clark Aposhian, a gun lobbyist with the Utah Shooting Sports Council, said KSL.com obviously decided it was worth keeping the firearms listings and said there was no reason for the site to not continue with the current policy.
"No one study has shown KSL or like sites or private transfers of firearms are responsible for the firearms used in crimes," Aposhian said. "I'm not going to say never has a firearm purchased through KSL been used in a crime, but it's certainly not a pattern. It's the exception."
O Listen to the audio of one of the online gun-sale negotiations recorded by a private investigator: http://bit.ly/vmlvII
Plus • Additional information about the Mayors Against Illegal Guns is available here: http://bit.ly/rzYmPZ