An attorney for the NBC television network told investigators that staffers misinterpreted conflicting information from D.C. and federal authorities when seeking permission to use an empty, 30-round gun clip as a prop on “Meet the Press.”

.A two-page letter from the lawyer, Lee Levine, to the D.C. attorney general, makes public for the first time how the show’s host, David Gregory, says he got hold of the high-capacity ammunition magazine, which even empty is illegal to possess in the District.

The letter was made public on Tuesday by the Attorney General’s office, which declined to file charges against Gregory, following a Freedom of Information Act request filed by The Washington Post. The office also released dozens of letters by people angry with its decision, but declined to make public other documents.

Levine, who also represents The Washington Post’s online magazine Slate, wrote to the District’s attorney general, Irvin B. Nathan, that NBC “borrowed the empty magazine from a private citizen who lives outside the District of Columbia.” The letter says the intent was only to “illustrate for viewers” the “substantial public debate and news coverage” over guns.

Levine wrote that on Dec. 21, NBC consulted with a spokesperson at the federal Bureau of Alcohol, Tobacco, Firearms and Explosives “and was advised that the use of an unloaded magazine would be permissible.” The attorney added that network officials believed that the ATF official had consulted D.C. police “before providing this advice.”

The network made the same inquiry to a spokesperson in the D.C. police department on the same day, Levine wrote. That spokesperson advised NBC that the District “prohibits the possession of a high capacity magazine and suggested the program instead use a photograph.” The crime is a misdemeanor punishable by up to a year in jail and a $1,000 fine.

Levine wrote Nathan that the network ”incorrectly interpreted the information it received from ATF and the MPD.”

D.C. police have previously acknowledged informing NBC that showing the clip would be illegal. An ATF official confirmed Levine’s account. A spokeswoman for NBC declined to comment.

Gregory has not made any statement about the issue since he held the clip during a Dec. 23 interview with the National Rifle Association’s executive vice president, Wayne LaPierre, while discussing the school shootings in Newtown, Conn.

Viewers called D.C. police as the show aired to demand they arrest Gregory. The police then announced an investigation, which ended Jan. 10, a day after the letter from Levine was sent, when Nathan said that he would not prosecute Gregory.

Nathan sternly warned the network “of the gravity of the illegal conduct,” but he wrote that he decided to exercise “prosecutorial discretion” in not pursuing a criminal case. He explaining in his letter that “prosecution would not promote public safety in the District of Columbia, nor serve the best interests of the people.”

D.C. Police Chief Cathy L. Lanier supported Nathan’s decision, saying of NBC, “I think they very narrowly dodged a bullet in this case.”

Critics pounced on Nathan’s decision, sending scores of letters to his office complaining that the prosecutor was unfairly enforcing two standards with the law — one for regular citizens, another for a well-known journalist who interviewed President Obama in the White House during the course of the investigation.

“I am going to be coming to Washington in Mid-February, and as I am a firm believer in 2nd amendment rights,”one person wrote Nathan. “I wanted to find out if I needed any permits to bring my AR-15 with me, to use as a teaching tool while I visited various public institutions? I understand that NBC’s David Gregory was given an exemption from any DC firearms laws for his teaching moment and I was hoping to get my own exemption.”

Another person wrote Nathan, “I find this lack of prosecution troubling because the DC police were asked about the magazine, to which they said “no.” Yet David broke the law anyway in front of thousands of television viewers.”