A key militant involved in the 2012 attacks on the U.S. diplomatic compound in Benghazi, Libya, arrived in Washington, D.C., on Friday and is set to appear before a U.S. District Court judge.

Mustafa al-Imam was captured by special operation forces on Sunday after the Trump administration and the Libyan government signed off on the joint mission.

Al-Imam's initial court appearance is set for 4 p.m. Friday.

President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE announced his capture on Monday.

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"The United States will continue to support our Libyan partners to ensure that ISIS and other terrorist groups do not use Libya as a safe haven for attacks against United States citizens or interests, Libyans, and others," the president said in a statement.

"To the families of these fallen heroes: I want you to know that your loved ones are not forgotten, and they will never be forgotten," he continued.

Al-Imam allegedly played an integral role in the attack, which occurred on Sept. 11, 2012, and led to the deaths of Ambassador Christopher Stevens and three other Americans.

CNN has reported that the U.S. government has video of al-Imam at one of the two sites of the attacks and that the militant could have been operating under different aliases at the time.

The attacks have become politically significant, with Republicans often slamming Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE, who was secretary of State at the time, for her response.

Various Republican congressional panels spearheaded probes into the attacks and often slammed the Obama administration for not cooperating.

Trump, who has also hit Clinton and the Obama administration for their responses, said in 2012 that the attack was "bigger than Watergate."