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Washington police are investigating whether NBC's David Gregory broke the law by holding up what appeared to be a 30-round gun magazine on Sunday's Meet the Press after the network apparently got conflicting opinions about whether it would be legal for him to do so.

It is illegal in the district to possess a "large capacity ammunition feeding device."

Gwendolyn Crump, director of the Office of Communications for the Washington Metropolitan Police Department, told ABC News, "NBC contacted MPD inquiring if they could utilize a high capacity magazine for their segment. NBC was informed that possession of a high capacity magazine is not permissible and their request was denied. This matter is currently being investigated."

But ABC News has learned from an official at the Bureau of Alcohol, Tobacco, Firearms, and Explosives that NBC had reached out to the federal agency on Friday for advice before displaying the weaponry.

According to the ATF official, the agency noted that ATF doesn't enforce D.C. gun laws, but agreed to put the question to a couple of Washington police officers who've worked with the agency in the past.

The D.C. officers advised the ATF spokesman that Gregory could display the magazine, provided it was empty, the source said.

That turned out to be bad advice, as conservative media and gun rights activists were first to note. The ATF official describes this as a "misunderstanding," and says he hopes DC police will not bring charges.

Another Washington DC police officer and spokesperson Tisha Gant said the situation was "being investigated," but would give no other details including what exactly is under investigation.

A section in the D.C. criminal code says "no person in the District shall possess, sell, or transfer any large capacity ammunition feeding device regardless of whether the device is attached to a firearm." The section stipulates that "the term large capacity ammunition feeding device means a magazine," or similar devices.

Gregory held up what looked like a 30-bullet gun magazine when interviewing the National Rifle Association's executive vice president and CEO Wayne LaPierre on Sunday. Gregory pressed the NRA head on whether fewer children would have been killed during the Sandy Hook Elementary shooting on Dec. 14th if the shooter had access to less ammunition.

Since the interview, conservative media and gun rights activists said that Gregory appeared to have violated the district's gun law. Police subsequently confirmed they were investigating.

NBC News declined to comment through a spokesperson.

ABC News' George Sanchez contributed to this report.