Benghazi militia leader charged in U.S. consulate attack once dared Libya gov't to "come to my house and arrest me"

Benghazi attack: Criminal charges filed again... 01:49

(CBS News) Nearly a year after the deadly attack on the U.S. diplomatic mission in Benghazi, Libya, federal prosecutors have filed the first criminal charges related to the assault that killed four Americans, including Ambassador Chris Stevens.

The Department of Justice is keeping the charges against the suspect, Libyan militia leader Ahmed Abu Khattalah, under seal, but CBS News' Margaret Brennan reports that the suspect has been living openly in Benghazi since the September, 2012 attack.

Khattalah admitted to CBS News last fall that he was at the scene on the night of the attack, but denied a personal role in the violence.

"I went to help four men who were trapped inside," Boukhatala told CBS News correspondent Elizabeth Palmer. When he arrived, though, the men were gone, according to the Islamist militant.

At the time, Libya's government had told CBS News that Boukhatala was a "prime suspect" in the attack on the U.S. offices, but asked about that accusation by Palmer, the militant smiled and said, "if that's what the President is saying, then he should come to my house and arrest me."

But that's something Libya's government security forces wouldn't have dared to do. Khattalah is the chief of a ferocious militia in Benghazi, the Abu Ubaidah Brigades - a sub-group of the larger Ansar al Shariah militia.

Palmer reported that the militia -- armed to the teeth with weapons looted from deposed dictator Muammar Qaddafi's arsenals -- acted at the time of the attack as both military and police in parts of Benghazi. The government's security forces, the official police and army, are simply too weak to push them out.

Khattalah told Palmer that the attackers were merely ordinary people armed with rocket-propelled grenades and added that he expected a fight should the government move to arrest Islamist militia members suspected in the attack.

It remains unclear whether the U.S. has now asked Libyan authorities to arrest Khattalah or whether the FBI has identified the other suspects, pictured alongside Khattalah in a series of photos taken from the security cameras at the consulate. The other men are thought to be members of Khattalah's militia. Neither the militia nor Khattalah have been specifically identified by the U.S. government as terrorists, according to Brennan.

"The investigation is ongoing. It has been and remains, a top priority," Justice Department spokesman Andrew C. Ames said Tuesday.

However, the FBI has not made any arrests in the 11 months since the attack and the Obama Administration faces mounting pressure to take action. Last week, a small but vocal group of eight Republican congressmen sent a message to the newly-confirmed FBI Director James Comey, pressing him to take action.

In the letter, initiated by Sen. Lindsey Graham (R-S.C.) and Rep. Jason Chaffetz (R-U.T.), the legislators called the administration's investigation thus far "unacceptable" and called for an "aggressive" investigation."