The ranking Democrat on the House Oversight and Government Reform Committee blasted the panel’s chairman for making “baseless accusations” and insulting the integrity of the FBI investigators probing the murder of a federal agent.

Rep. Elijah Cummings (D-Md.) said on Monday night that Rep. Darrell Issa’s (R-Calif.) comments over the weekend were “unbelievably reckless” and inaccurate with what federal officials have told the committee in closed settings.

Border Patrol Agent Brian Terry was killed in December in an Arizona firefight. Two of the weapons found at the scene were sold to suspected straw buyers for Mexican drug cartels under Operation Fast and Furious — a botched gun-tracking operation — but ballistics was unable to determine whether the guns were used to kill Terry.

Issa believes there was a third gun recovered at the scene and in the FBI’s possession that may have been the murder weapon, but Cummings and the Department of Justice (DOJ) say that is not the case.

“It is unbelievably reckless for Chairman Issa to go on national television and repeat these baseless accusations, which attack the integrity and credibility of entire law enforcement agencies and undermine the prosecution of those responsible for Agent Terry’s death,” Cummings said. 

“In a closed briefing with committee staff earlier this month, the FBI dispelled any allegation that they recovered a third gun at the scene, and the committee has no evidence to the contrary,” Cummings said.

On Sunday, Issa told CBS’s Face the Nation that while he was not suggesting the FBI tampered with evidence at the scene of Terry’s murder, he was very concerned that the FBI and the Justice Department (DOJ) have not been informing Congress of all the vital information necessary to understand who was responsible for Terry’s slaying.

“We're not accusing any one of a criminal cover-up, but we have a real obligation to the Terry family and a real obligation to the Constitution to follow this to ensure that [the] Justice Department in all of its tentacles in law enforcement do the kind of job that witnesses who came from there said they want to do and they always do,” said Issa.

Issa said that Kenneth Melson, the former acting director for the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) — which oversaw Fast and Furious — has indicated that the agency has not always been as forthcoming as it could be and that they’d rather handle things internally.

“Kenneth Melson and other cooperating witnesses have made it clear that there is a general pattern of playing a shell game with Congress, we'll take care of this ourselves,” said Issa.

“And as you know, the FBI has a history in some cases of working with felons and criminals and hiding their other crimes in order to keep an investigation going,” Issa said.

“We thought that was behind us but it might not be,” he said.

DOJ also issued a statement on Monday night saying that Issa’s comments were offensive and misunderstood how the FBI catalogues evidence found at crime scenes.

“The FBI has made clear that reports of a third gun recovered from the perpetrators at the scene of Agent Terry’s murder are false,” said the DOJ in a statement.

"Unfortunately, this most recent false accusation not only maligns the dedicated agents investigating the murder of Agent Terry, it mischaracterizes evidence in an ongoing case,” the DOJ said.

Issa contends that since the two weapons found at Terry’s murder scene were catalogued as “K2” and “K3,” there must be a “K1” -- that is, a third gun which has never been revealed to lawmakers or their investigators. The DOJ has said that the “K1” is a sample of Terry’s blood and not another weapon.

Issa’s assertions are the latest in his investigation into Fast and Furious, a botched operation launched in 2009 in an attempt to track sales of weapons to known and suspected straw buyers for Mexican drug cartels in the Southwest region.

The hope was to dismantle the gun trafficking routes but agents were told to not provide the guns or their buyers with adequate surveillance, allowing thousands of weapons to disappear into the hands of suspected and known criminals.