The Justice Department is accusing the Republican congressman who is leading an investigation into "Operation Fast and Furious" of "mischaracterizing evidence" and "maligning" federal law enforcement officials by questioning Sunday whether the FBI was trying to cover up the existence of a third gun at the scene of Border Patrol agent Brian Terry's murder last year.
"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," the department said in a statement Monday.
This comes one day after Rep. Darrell Issa, R-Calif, chairman of the House Oversight and Government Reform Committee, appeared on a Sunday morning news show and noted that a now-public FBI ballistics report labeled two guns tied to "Fast and Furious" as "K2" and "K3," but "there's no 'Ticket 1.'"
"One weapon has a '2,' one has a '3,' on it. There's no '1,'" Issa said on CBS. "When agents who were at Brian Terry's funeral made statements to his mother indicating that there were three weapons, when the two weapons that they have tested don't conclusively match up [to the bullet that killed Terry], then you look and say, 'Well, was there a third weapon at the scene?'"
Asked why the FBI would make such a move, Issa said the agency "has a history in some cases of working with felons and criminals and hiding their other crimes in order to keep an investigation going."
In its statement late Monday, the Justice Department offered its first public explanation of "K1."
"According to the FBI, the item that Chairman Issa refers to as 'K1' is a blood sample from Agent Terry, not a firearm," the statement said. "For this reason, it was not listed on the ballistics report prepared by the FBI."
The Justice Department said law enforcement officials refer to some items seized at scenes as "known" items -- or "Ks" for shorthand.
"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 Justice Department said in its statement Monday night.
Rep. Elijah Cummings of Maryland, the ranking Democrat on Issa's committee, also criticized Issa for fueling what he called "baseless speculation" about tampered evidence.
"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.
But an Issa spokesman said the Justice Department is playing “word games” and has not answered whether officials with the department suspect one of the two guns they cite was used to kill Terry, or if there was another weapon to blame.
“If there was no third gun, then Agent Brian Terry was killed by a weapon from Operation Fast and Furious," the spokesman said. "The Justice Department has so far failed to acknowledge this or provide appropriate answers.”
Monday's statement is the latest in a broader back-and-forth over tactics used by ATF investigators to target major gun-runners in Arizona. Launched in late 2009, "Fast and Furious" investigators planned to follow gun purchasers in hopes that suspects would lead them to the heads of Mexican cartels. But high-powered weapons tied to the investigation ended up at crime scenes in Mexico and the United States, including that of Terry's murder in December 2010.
In its statement, the Justice Department said Issa's staff had been told "there were two - not three - guns recovered" from the scene.
For weeks -- as speculation over a third gun spread and some accused the FBI of trying to protect a confidential informant -- the FBI has insisted as much in statements to news outlets.
In addition, an ATF "briefing paper" about the murder, obtained by Fox News and sent to top Justice Department officials in Washington two days after the incident, said that "during the search of the area two ... AK-47 rifles, serial numbers 1983AH3977 and 1971CZ3775 were recovered near the scene of the shooting."
But emails in the hours after the incident show at least some ATF officials wondered whether a third gun had been recovered.
In one email, deputy ATF-Phoenix director George Gillett asks if two AK-47 rifles cited were "in addition to the gun already recovered this morning." It's unclear whether anyone responded to him.
Since then, some sources have accused the FBI of covering up evidence to protect an informant working inside a major Mexican cartel. That informant, sources have alleged, helped pay for the weapons used in the attack that killed Terry.
In addition, in recently disclosed recordings, a lead ATF investigator can be heard telling a Phoenix-area gun-dealer that an "SKS assault rifle out of Texas" had been found at the Terry murder scene.
In September, a spokeswoman for Sen. Charles Grassley, R-Iowa, told Fox News it was "pretty clear" the ATF agent was talking about the Terry murder. Still, weapons involved in another case not tied to "Fast and Furious" -- the murder of Immigration and Customs Enforcement agent Jaime Zapata in Mexico -- were traced to Texas.
The recordings are part of what led Issa and Grassley to state in a June report on “Fast and Furious” that authorities responding to the scene of Terry's murder in fact "recovered three weapons from the suspects, who had dropped their rifles in order to flee the scene faster." On Sunday, Issa posed it as a question: "Was there a third weapon at the scene?"
Fox News' William LaJeunesse contributed to this report