WASHINGTON - The trial of the accused mastermind of the September 2012 attacks that killed four Americans at a U.S. special diplomatic mission and CIA annex in Benghazi, Libya, will turn this week to testimony by two active CIA security force operatives, another who was at the assault and the widow of another killed in the assault. Beginning Tuesday under unusual security measures, two CIA witnesses will testify under the pseudonyms "Edwards" and "Charles" in a courtroom closed to nearly everyone but the defendant, Ahmed Abu Khattala, 46; the lawyers for each side; jurors; U.S. District Judge Christopher R. "Casey" Cooper of Washington; and courtroom personnel, according to in-court discussions last week among Cooper, prosecutors and defense lawyers.As has been done since the trial started Oct. 2, a live audio stream of the pair's testimony will be fed to two other rooms at the federal courthouse in Washington for observers, including journalists.Video feeds that have been provided in the ancillary rooms will continue to show the judge, attorneys, exhibits and defense table, but a camera showing the witness stand will be turned off during the testimony by the two active CIA security operatives, prosecutors said. Prosecutors described the upcoming testimony as coming from "OGA" witnesses - a shorthand for "other government agency" that generally is used as a reference to the CIA. The role of CIA security personnel and the location of the annex have already been acknowledged in court filings and in open court at Abu Khattala's trial. The Justice Department asked for the closed hearing to protect the men's identities because they continue to work as secret, undercover security for the agency, prosecutors said. Courts in the past have allowed CIA witnesses to testify behind partitions or while wearing light disguises, such as wigs, false beards or eyeglasses.Cooper approved another atypical request - to which the defense agreed - to allow "front office" representatives of the pair's employer to sit in the courtroom for the testimony because of the organization's stake in the trial. Court transcripts of the discussions about that request show that each side thought having some people sitting in the public benches in the courtroom might avoid signaling to jurors that the courtroom had been cleared for a special purpose, a cue that could be prejudicial if it affected how jurors weighed the testimony they then would hear.The court released transcripts of last week's proceedings Friday.The transcripts include muffled conversations at the bench that are out of earshot of the jury and of anyone sitting in court, but become part of the public court record. The transcripts also include other discussions - that occur in front of any trial watchers but after jurors have been moved out of the courtroom - in which the parties in the case and the judge hash out scheduling and trial administrative matters. Prosecutors also are posting exhibits that have been introduced at the end of each trial day.The CIA's secret contractor security force, called the Global Response Staff, guarded the annex and helped protect the mission, where U.S. Ambassador J. Christopher Stevens and State Department communications aide Sean Patrick Smith were killed, witnesses and prosecutors have said in court. GRS members Glen A. Doherty and Tyrone S. Woods died at the annex, where they fought alongside other GRS and State Department security personnel.Abu Khattala, a Libyan national who led a brigade of the Ansar al-Sharia militia, which the United States has designated a terrorist organization and holds responsible for the Benghazi attacks, has pleaded not guilty to 18 charges including conspiracy to support terrorism, murder, attempted murder and damaging U.S. facilities. He faces life in prison if convicted.The trial is set on Wednesday to hear again from the State Department's chief regional security officer at the small, special diplomatic mission in Benghazi at the time, Alec Henderson.He had testified for several hours before the trial broke Thursday for the weekend and the federal holiday Monday. The federal trial in Washington, five years after the attacks, returns a focus to the criminal prosecution in an episode that became a political lightning rod during last year's presidential campaign for Hillary Clinton, who was secretary of state in 2012.It also poses a high-profile test of U.S. counterterrorism policies developed in recent years to capture alleged terrorists overseas and interrogate them for intelligence purposes, while preserving the right to prosecute them in civilian court.Abu Khattala was captured in Libya by U.S. commandos in June 2014.Henderson has given the 15-member Washington jury - 12 plus three alternates - a blow-by-blow account of the attacks the night of Sept. 11 and Sept. 12, 2012, using excerpts of closed-circuit video surveillance from multiple security cameras around the Benghazi diplomatic mission, which was overrun starting at 9:42 p.m. The CIA's secret post, to which GRS and State Department security personnel evacuated afterward, subsequently came under attack after midnight. Outside the presence of the jury, defense attorneys said Thursday that they were waiting for the government to disclose to them unspecified but agreed-upon snippets of classified documents for Henderson's cross-examination.In the transcripts, prosecutors said they expect testimony later this week from Dorothy Narvaez Woods, a Navy veteran, University of Maryland-educated dentist and the widow of Tyrone S. Woods. Also expected is testimony by GRS member and U.S. Marine Corps veteran John "Tig" Tiegen, 41, prosecutors said.Tiegen will testify openly because his name is well-known, prosecutors said, identified in a feature film and book about the Benghazi incident co-written by several GRS members. GRS contractors provided security to CIA staff seeking to track Libyan stockpiles of rocket-propelled grenades and other weapons. They also backed up a low-profile and lightly staffed State Department special mission that Stevens used when in Benghazi. It relied on a handful of U.S. diplomatic security agents and a larger Libyan contract force.Last week, in poignant testimony, Peter Sullivan, who is married to Stevens's sister, Ann Stevens, recalled his brother-in-law as a dedicated "man of peace."Stevens was "trying to forge a coalition among factions" in Libya, Sullivan recalled the ambassador saying, including a description he said Stevens relayed roughly as working with "about 156 [groups] with an average of seven people trying to put together a government.""He roamed a lot of the land. He moved around with little security, to some people's objection, but that's the way he was. He was a man of peace," Sullivan said. "He got something like 40,000 letters from Libyans after his death. They loved him there."