CBS: FBI hiding facts on "Fast and Furious" scandal?

The House Oversight Committee plans to ask the FBI whether all the guns that were used to kill a federal agent are accounted for. Sharyl Attkisson reports on the latest of the fallout from the "Fast and Furious" operation.

The head of the House Oversight Committee, Rep. Darrell Issa, said he plans to send a letter to the FBI this week to ask about apparent discrepancies in the investigation of a murder related to "Fast and Furious," the government's controversial "gunwalking" case, CBS News investigative correspondent Sharyl Attkisson reports.

U.S. Border Patrol Agent Brian Terry was gunned down near the U.S.-Mexico border last December, and at least two assault rifles from the Bureau of Alcohol, Tobacco, Firearms and Explosives' Fast and Furious case were found at the scene.

That focused blame on the controversial ATF operation that monitored suspects who trafficked the weapons instead of arresting them and seizing the guns.

But 10 months after the murder, there are questions about how many weapons the FBI recovered at the scene and other key details.

On CBS' "Face the Nation" Sunday, Issa, R-Calif., told moderator Bob Schieffer there's reason to ask whether there's a third, missing weapon.

(Watch at left)

"When agents who were at Brian Terry's funeral made statements to his mother indicating that there were three weapons ... then you look and say, well was there a third weapon at the scene?" Issa asked. "Were there additional people who escaped with weapons?"

Also, a ballistics report turned over to Congress mentions just two rifles, saying it "could not be determined" if one of them fired the bullet that killed Terry.

There's also talk of a third weapon, called an "SKS" rifle, in secret recordings obtained by CBS News. In the following partial transcript of a March 2011 conversation, the lead ATF case agent on Fast and Furious is speaking to a gun dealer who cooperated in selling weapons to suspects.

Gun dealer: "There's three weapons."
ATF agent: "There's three weapons."
Dealer: "I know that."
Agent: "And yes, there's serial numbers for all three."
Dealer: "That is correct."
Agent: "Two of them came from the store."
Dealer: "I understand that."
Agent: "There's an SKS that I don't think came from ... Dallas or Texas or something like that."

The FBI wouldn't comment but has implied in the past that there was no third gun. Issa said he's seeking clarity and that, until key questions are answered, it fuels speculation.

The FBI has kept nearly everything about Terry's murder secret, saying that releasing anything would jeopardize their investigation, now beginning its eleventh month.