Two Republican congressmen who posed for a photo with an AR-15 assault rifle may soon find themselves under investigation after District of Columbia police Tuesday were given “materials,” including the Twitter photo that could be used to make a case against them, the Hill reported. Reps. Trey Gowdy, R-S.C., and Ken Buck, R-Colo., posed for the photo tweeted on Buck’s account last Thursday:

Assault rifles like the AR-15 are banned in D.C. The weapon belonged to Buck, who told the Hill that the gun was “inoperable” and he cleared the firearm with Capitol Police before hanging it up in his office. “I have a very patriotic AR-15 hanging in my office. It hangs directly above my Second Amendment flag,” he said. “While safety protocols call for all guns to be treated as if they are loaded, this one isn't. Further, a close inspection of the only public photo of the rifle will show that the bolt carrier assembly is not in the rifle; it is in fact in Colorado.”

The photo raised the alarm of the Colorado site ColoradoPols Friday, a day after Buck posed with the AR-15 and Gowdy, the chairman of the House Select Committee on Benghazi. “Short of a really good explanation we can’t think of right now – or, we suppose, the possibility this photo was taken across the Potomac in Virginia – we assume the D.C. Metropolitan Police will want to have a little chat with Rep. Buck about this,” the website wrote.

The D.C. U.S. attorney’s office said it gave “materials” about the photo to local police. "The matter has been referred to the Metropolitan Police Department for further investigation,” an office spokesman told the Hill.

The incident marked the second time in two years that a public figure attracted scrutiny over an assault rifle or ammunition in the capital. David Gregory, then the moderator of “Meet the Press,” was considered for charges by D.C. police after he showed an assault rifle magazine on television. The show is taped in D.C., but police ultimately decided not to file charges despite NBC warning Capitol Police it was going to show the magazine and the network being told that to do so would be against the law.