The U.S. diplomatic mission in Benghazi is seen in flames Sept. 11, 2012. (ESAM OMRAN AL-FETORI/REUTERS)

The conviction Tuesday of Libyan militia leader Ahmed Abu Khattala on terrorism charges — but not murder — in the 2012 Benghazi attacks would not weaken efforts to try a second defendant in Washington or the potential prosecution of future suspects, current and former FBI and Justice Department officials said.

Carlos T. Fernandez, a former senior FBI counterterrorism official whose New York City-based agents investigated the attacks in which four Americans were killed, said the potentially lengthy prison sentence facing Abu Khattala, the only person prosecuted to date in the attacks, marked a victory for investigators and prosecutors.

"Tremendous creative work was done by the FBI and prosecutors with the U.S. attorney's office of the District to get these charges, in an environment where no one was willing to take any risk," Fernandez said. "This certainly isn't going to stop any of their efforts."

"I feel confident they will continue pursuing each and every lead for as long as they possibly can," he said, adding that investigators and prosecutors "are limited only by the ability of their leaders in terms of getting the job done."

At least eight of Abu Khattala's militia members were caught on U.S. surveillance video at the two attack scenes — a U.S. diplomatic compound and a nearby CIA annex — according to evidence shown at the trial in Washington. Abu Khattala himself identified three dozen individuals to FBI interrogators, the court heard in testimony. At the time that U.S. commandos captured him in Libya in 2014, U.S. officials said more than a dozen others had been charged in a sealed complaint.

Fernandez's comments came as Acting Assistant Attorney General Dana Boente said after Tuesday's verdict in Washington that the Justice Department "will not rest" in its pursuit of others involved in the attacks that took place overnight Sept. 11 to Sept. 12, 2012. Scores of militants overran and set fire to the U.S. diplomatic mission and fired mortars at the nearby CIA facility, killing U.S. Ambassador J. Christopher Stevens and fellow Americans Sean Smith, Tyrone S. Woods and Glen Doherty.

The White House set a tone similar to Boente's when it approved federal prosecution of a second Libyan suspect, Mustafa al-Imam, whose capture President Trump announced Oct. 29 had been carried out "on my orders." The president added: "Our memory is deep and our reach is long, and we will not rest in our efforts to find and bring the perpetrators of the heinous attacks in Benghazi to justice."

Imam has pleaded not guilty.

The Trump administration's high-level endorsement of a second civilian trial and the hunt for suspects comes amid a seeming shift in Congress since the 2010 federal trial of Ahmed Khalfan Ghailani. The former Guantanamo Bay detainee was acquitted of all but one count of conspiracy in the deaths of hundreds of people in the 1998 bombings of two U.S. embassies in Kenya and Tanzania.

Ghailani was imprisoned for life, but senior Republican lawmakers called for the abandonment of civilian trials for foreign terrorism suspects.

A courtroom sketch from Oct. 2, 2017, shows Ahmed Abu Khattala listening to an interpreter through earphones at his trial in federal court in Washington. (Dana Verkouteren/AP)

By comparison, several past congressional supporters of trial by military commissions declined to comment on the Imam case and the Abu Khattala verdict. That group of lawmakers includes Sens. John McCain (R-Ariz.) and Lindsey O. Graham (R-S.C.), chairman and member of the Senate Armed Services Committee, respectively, and Rep. Peter T. King (R-N.Y.), a member of the House Homeland Security Committee.

A District jury deliberated for five days before finding Abu Khattala, 46, guilty of conspiracy and providing material support to terrorism, malicious destruction of the U.S. special diplomatic mission in Benghazi and a firearms violation, but acquitted him of several murder and attempted-murder counts and of attacking the CIA annex.

Abu Khattala, who led an extremist-Islamist brigade, faces at least 10 years and up to life in prison at sentencing early next year before U.S. District Judge Christopher R. Cooper of Washington.

One reason the acquittals in the Abu Khattala case may not have been seized on by critics of civilian prosecution of terrorism suspects is that Abu Khattala will still "almost certainly" face an exceptionally long sentence, and because of the lack of a realistic alternative, said Robert Chesney, a University of Texas law professor who specializes in national security.

Military commissions have a worse track record, he said, noting new problems just this month in a Guantanamo Bay case involving detainee Abd al-Rahim al-Nashiri, who is accused of masterminding the deadly bombing of the USS Cole in a Yemeni harbor in 2000.

It also is "far from clear," Chesney added, that the government can show that Benghazi suspects are eligible for detention at Guantanamo Bay by virtue of being "enemy combatants" or members of groups with which the United States is at war, such as al-Qaeda.

Still, the Abu Khattala verdict did not satisfy some of those most affected by the attacks, including CIA security contractors who defended the U.S. facilities, some of whom have called the trial a political show.

One CIA security operator injured in the attack, Mark Geist, tweeted Tuesday that it was "an honor" to testify at the trial and as what he called a voice for fallen comrades Woods and Doherty.

"As for Abu Khatala he thinks he will be Martyred. He will have to enter a greater court, give an account to a greater judge and no doubt will receive a greater sentence," Geist said in his tweet.

Alice Hunt Friend, who was a Pentagon official working Africa security policy from 2009 to 2014, said it is important to distinguish between the goals of trials and the objectives of ongoing, real-time intelligence and military counterterrorism efforts in Libya and the wider region.

"What these kinds of trials allow the U.S. government to do is hold individuals accountable for illegal acts. . . . That is separate from military operational goals," Friend said. "The focus of the United States in Libya today is more about Islamic State," she said, than about the shifting assortment of Abu Khattala's and other Islamist militant groups in the country five years ago.