Mayor Bloomberg’s headline-grabbing stunt of sending private eyes on “sting” operations against out-of-state gun dealers has turned into an embarrassment. The mayor sent amateurs off to play “cops,” without bothering to coordinate with the Bureau of Alcohol Tobacco, Firearms & Explosives or his own police department.

While announcing his lawsuit against 15 gun dealers, the mayor said ATF was “asleep at the switch.” He implied the same in his recent congressional testimony. Those comments are insulting to the hard-working men and women of ATF.

Far worse than verbal insults, reports indicate his sting operation has jeopardized over a dozen ongoing criminal investigations, putting law enforcement officers at risk. A suspect who suddenly finds out that a gun store he frequents is under surveillance will likely stop his activities. He also could violently turn on anyone he believes is an investigator; shop owners and employees are potential targets, too. The few gun storeowners who are corrupt will be on their best behavior. Suspects and evidence may disappear, with weeks or months of investigative work being lost.

Having already interfered in ongoing investigations, the mayor belatedly turned its information over to the ATF New York Field Division. ATF has said it will investigate both the dealers involved and the mayor’s private eyes to determine whether anyone broke the law. If dealers are violating the law, they should be put out of business or prosecuted, and ATF is the appropriate agency to do it. And the same goes for the private eyes.

ATF enforces our nation’s firearms laws, regulates federally licensed firearms dealers, conducts inspections and, if it suspects wrongdoing, investigates and arrests anyone, including dealers, who breaks the law. ATF has a long history of working closely with NYPD to trace firearms recovered by the police to investigate and arrest illegal firearms traffickers.

The number of defendants referred by ATF for prosecutions is up 170% since 2000, with a 14% increase in the number of convictions for illegal firearms trafficking in just the past year. ATF is not “asleep at the switch,” and the people of New York need to know it.

The city’s lawyers selected the dealers to go after as part of the mayor’s lawsuit by using law enforcement gun trace data acquired before Congress put such records off limits to all but law enforcement. These restrictions must remain in place to prevent ATF’s national firearms trace database from being misused in the public domain. The ill-considered use of trace data – like conducting private investigations – can be dangerous. If this data is available to the public, firearms traffickers will get their hands on it too. Realizing a risk to law enforcement, Congress in 2003 restricted access to the data to law enforcement, saying it “holds the potential of endangering law enforcement officers and witnesses, jeopardizing on-going criminal investigations ….”

New York Police Commissioner Ray Kelly expressed similar concerns telling the United States Attorney General in a 2002 letter that the release of trace information to the public would “seriously jeopardizes not only the investigations, but also the lives of law enforcement officers, informants, witnesses, and others.” Ironically, although Mr. Bloomberg complained to Congress about restrictions on the public dissemination of trace data, his misuse of that data, and the subsequent disruptive and potentially dangerous effect of his undercover operation on ongoing federal investigations may have proven the wisdom of Congress’ judgment.

Criminal firearms violence is a problem that ATF attacks vigorously, with assistance and cooperation from local law enforcement and the firearms industry. ATF is equipped to handle it. The city should let it.

Mr. Nelson retired from the Bureau of Alcohol, Tobacco, Firearms and Explosives in 2005 as a deputy assistant director.