Mayors Against Illegal Guns, a group of more than 550 U.S. mayors, is calling for a background check system that will keep guns out of the hands of dangerous people. (I know here in Philadelphia, mayors have been continuously stymied by the NRA-owned state legislature every time they try to put even small roadblocks in the way of gun purchase on demand.)

To make a point, NYC for the second year sent undercover investigators to one of the largest Phoenix gun shows -- two weeks after Rep. Gabby Giffords was shot -- to illustrate how easy it is to use the gun show loophole to illegally buy weapons:

On January 23, 2011, undercover investigators working for the City of New York attended the Crossroads of the World gun show in Phoenix. One investigator purchased a Glock 9 mm semiautomatic pistol without a background check. Because the gun dealer is a private seller and not a federally licensed firearms dealer, no background check was required and the transaction was apparently legal, assuming the seller was, in fact, an “occasional seller.” This gap in federal law that enables private sellers to sell guns without background checks is sometimes called the Gun Show Loophole because such sellers congregate at gun shows. The investigator also purchased 33-round extended magazines for the Glock from a separate seller – also legal because the 1994 law that banned such sales expired in 2004.

Gun shows have been found to be major sources of guns used in crimes. According to the ATF, 30 percent of guns involved in federal illegal gun trafficking investigations are connected to gun shows. Because no records are kept, guns sold by private sellers at gun shows become virtually untraceable.

Two private sellers failed integrity tests by illegally selling guns to an undercover investigator. Each seller sold a 9 mm semiautomatic pistol, one Sig Sauer and one Smith & Wesson, to an undercover investigator even after he declared that he “probably couldn’t pass” a background check. That statement should have immediately stopped the sale because even though occasional sellers are not required to run background checks using the FBI database, it is a federal felony for them to sell guns to people they have reason to believe are prohibited purchasers.

In 2009, the City of New York conducted a similar investigation and documented problems at seven gun shows in three states. Investigators found private dealers who sold to those who said they could not pass a background check, including two sellers who failed at multiple shows. In total, 19 of the 30 private sellers approached in 2009 failed the test.

Since the 2009 investigation, four of the seven gun shows documented on video have changed their practices.

The operator of the Big Reno Show, and the owner of the venue, the Grand Sierra Resort and Casino, have each signed agreements with the City of New York agreeing to end no-background check gun sales. The Big Reno Show is one of the nation’s largest gun shows. It has 1,300 tables of exhibits, at the time of the investigation there were 120 private sellers at the show offering 1,700 guns for sale.

The operator of the Big Reno Show has also prevented any seller caught breaking the law in the undercover investigation from returning to the show. The agreement stipulates that all sales by private party sellers will be processed through licensed gun dealers who will perform background checks.

Bill Goodman’s Gun and Knife Shows promotes three of the seven shows visited by the City in 2009, they were held at the Hara Arena and Sharonville Convention Center in Ohio and at the Tennessee State Fairgrounds in Nashville. The promoter has ended no-background check sales at all 34 shows that he promotes.

In 2009, the City turned over all of its investigative materials on illegal sales to the Bureau of Alcohol, Tobacco Firearms and Explosives (ATF). One of the sellers caught on tape at the Big Reno gun show, Robert Daly, was the subject of an ATF search warrant in July 2010. When the warrant was executed at Daly’s home in Mesa, Arizona, ATF agents seized 799 guns. The Justice Department has charged him with illegally selling these guns at gun shows.

Yep. Even if you're selling hundreds of guns at gun shows, you're still considered to be a "private seller" and not a dealer. Isn't that nice? In light of recent events, even politicians have to see that it's time to keep guns out of the hands of high-risk buyers.

You'd think that Arizona, whose far-right activists are always screaming about horrific crimes allegedly committed by Mexicans sneaking across the border, would catch on to the concept that loose gun sale practices put all of us at risk. From last week:

In a case aimed at stemming the flow of U.S. weapons to the Mexican drug war, federal authorities indicted 20 men Tuesday on charges of buying an estimated 700 weapons in Arizona and conspiring to transfer them across the border, chiefly to the Sinaloa drug cartel.

The arrests, carried out by at least 100 federal agents, began early Tuesday, the latest crackdown targeting an international trafficking network that authorities say has seen as many as 60,000 weapons seized in Mexico and traced to U.S. sources.

Even if you don't care about your loved ones getting blown away, Arizona, maybe you could cut the rest of us a break.