U.S. forces have captured Mustafa al-Imam, a key militant in the 2012 Benghazi attack that killed Ambassador Christopher Stevens and three other Americans. From CBS News:

The commandos captured the man in Libya just before midnight local time on Sunday and are transporting him back to the U.S., officials told The Associated Press. The suspect is in the custody of the Department of Justice and is expected to arrive within the next two days on a military plane, according to one of the officials.

The officials said the mission was approved by President Donald Trump and done in coordination with Libya’s internationally recognized government. The officials, who weren’t authorized to speak publicly to the matter and demanded anonymity, would not say where exactly he was captured.

Trump and Secretary of State Rex Tillerson promised justice for the families who lost loved ones:

“The United States will continue to support our Libyan partners to ensure that [the Islamic State in Iraq and Syria] and other terrorist groups do not use Libya as a safe haven for attacks against United States citizens or interests, Libyans, and others,” Trump’s statement said, stressing that he plans to pursue the other “perpetrators of the heinous attacks.”

“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 added.

Secretary of State Rex Tillerson on Monday echoed that they will continue to track down those responsible for the attack.

“The Department of State family continues to mourn the loss of Ambassador Chris Stevens, Glen Doherty, Sean Smith, and Tyrone Woods, and we will spare no effort to ensure that justice is served for these dedicated Americans and public servants,” Tillerson said in a statement.

Attorney General Jeff Sessions said that his arrest is a huge step for the investigation and also promised justice. From CNN:

“We will never forget those we lost — Tyrone Woods, Sean Smith, Glen Doherty, and Ambassador Christopher Stevens — four brave Americans who gave their lives in service to our nation. We owe it to them and their families to bring their murderers to justice,” Sessions said in a statement.

Al-Imam used different aliases and the officials said he participated in the attack at one of the two sites, but did not specify which one.

The alleged mastermind of the Benghazi attack, Ahmed Abu Khatallah, is on trial in Washington, D.C. From Reuters:

In his opening statement, federal prosecutor John Crabb said Khatallah hates America “with a vengeance” and played a leading role in organizing the Sept. 11, 2012, attack on the U.S. diplomatic mission in Benghazi.

Khatallah “didn’t do the killing by himself,” he said. “He didn’t light the fires and he didn’t fire the mortars but you will hear he is just as guilty as the men who lit those fires and the men who fired those mortars.”

Crabb said that Khatallah “incited others to do his dirty work.” The Washington Times reported that the prosecutors put forth evidence in their opening statements, which included “snippets of security footage that showed Mr. Abu Khatallah walking into the Benghazi mission with an AK-47 in hand after the gates to the complex”

The prosecutors also said they have a lineup of witnesses that will testify against Khatallah and explain how he prepared for the attack. This includes one key witness that the U.S. paid a hefty price for.

Khatallah pleaded not guilty to 18 counts. These charges include “conspiracy, murder and material support of terrorists in the deaths of Stevens, State Department communications expert Sean Patrick Smith and security contractors Tyrone S. Woods and Glen Doherty.”