The U.S. consulate in Benghazi, Libya. (ESAM OMRAN AL-FETORI/REUTERS)

U.S. officials say efforts have stalled to capture about a dozen people secretly charged in the 2012 attack on the American compound in Benghazi that claimed the lives of U.S. Ambassador J. Christopher Stevens and three other Americans.

The individuals have been charged in sealed criminal complaints filed in federal court by the U.S. Attorney’s Office for the District of Columbia. They include one of the suspected ringleaders of the attack, Ahmed Abu Khattala, a militia leader with ties to ­al-Qaeda,­ said several U.S officials, speaking on the condition of anonymity because they were not authorized to discuss the case publicly.

So far, none have been brought to trial and the lack of progress in capturing Khattala has frustrated U.S. intelligence officials and lawmakers who want to see him and the others prosecuted. One official said that Khattala continues to operate in eastern Libya with impunity.

“He’s as free as a bird,” the official said.

In an interview, Rep. Mike Rogers (R-Mich.), who chairs the House intelligence committee, said the United States was not making a strong enough effort to capture Khattala.

“I don’t believe we have adequately resourced or operationally planned to remove Khattala or those involved in the Libyan 9/11 attacks,” Rogers said. “There are consequences for our lack of pursuit. . . . You have removed the notion of certainty in deterrence and you cannot lose that.”

Justice Department spokesman Andrew Ames and FBI spokesman Michael Kortan declined to comment on the case because it is the subject of an ongoing criminal investigation.

FBI Director James B. Comey has said that capturing suspects in the Benghazi case is a top priority for the FBI.

“It was the first matter I was briefed on which reflects the commitment within the FBI to that case and to bringing to justice those who were involved in the killing of our four folks,” Comey said in an interview with reporters a few weeks after he became director in September.

“We have worked very hard on it,” Comey said. “And it’s something that we are strongly committed to.”

Law enforcement officials said that the United States might have missed its best chance to arrest Khattala earlier this year. The U.S. intelligence community hatched a plan to snatch Khattala and an accused al-Qaeda operative, Nazih Abdul-Hamed al-Ruqai, known by his alias Anas al-Libi. The planning took months, requiring coordination between the FBI, the CIA and the Army’s elite Delta Force.

Libyan Prime Minister Ali Zeidan gave the go-ahead to grab Khattala and Ruqai, one U.S. intelligence official said. The plan involved nabbing Ruqai in Tripoli first and then Khattala, with both operations occurring within days of each other.

Ruqai was seized outside his home in Tripoli by U.S. military forces and taken out of the country to a U.S. warship for questioning. He was eventually flown to New York to face charges for the 1998 embassy bombings in East Africa.

Libyan government officials denied they knew about the raid and asked the U.S. government for “clarifications.” Zeidan said at a news conference that Libyan citizens should be tried in their home country and “Libya does not surrender its sons.”

The blowback was perhaps fiercer than expected. Days after Ruqai was seized, Zeidan was abducted but eventually released unharmed. The kidnapping of the prime minister only underscored the weakness of the current government and the power of militias in the country.

The Khattala mission was scrapped, and now any plans to remove him from Libya are on the back burner. The U.S. intelligence official said that the whereabouts of some of the other suspects are unknown.

“This situation is tougher in Libya now,” said a senior Obama administration official. “You sort of get one crack at these things, and then it’s tougher.”

Officials also stressed that another raid could lead to the toppling of Zeidan’s government and increase the chaos in a country that the United States would like to see stabilize.

Rogers said he did not buy that explanation.

“I don’t subscribe to that theory, and that is a theory,” Rogers said, referring to the idea that the Libyan government could fall.

Earlier this year, a seemingly unconcerned Khattala gave an interview to CNN at a coffee shop in Benghazi, saying that he had gone to the U.S. compound the night of the attack but was not involved in the violence.

Last month, government forces battled Khattala’s militant group, Ansar al-Sharia, in Benghazi, killing several and wounding dozens of others.