Prosecutors in the trial of the alleged Libyan mastermind of the 2012 attack in Benghazi that killed a US ambassador argued Thursday that he was equally responsible even if he did not personally take part.

Wrapping up final arguments in the trial of Ahmed Abu Khattala over the 2012 Benghazi attack, US government lawyers said he was guilty of conspiracy and murder in the deaths of US ambassador to Libya Christopher Stevens and three other Americans.

"'I will kill all the Americans, each and everyone of them...': This is what the defendant Abu Khattala said and this is exactly what he did," prosecutor Michael DiLorenzo told a jury in the trial in Washington federal court.

"On September 11, he took action," DiLorenzo said, highlighting that the attack in the eastern Libyan city took place on the anniversary of the 9/11 Al Qaeda attacks.

Khattala, in his 40s with a long white beard, sat passively in his chair in the courtroom, where his trial opened seven weeks earlier.

DiLorenzo summed up his argument that Khattala was an Islamic extremist who hated Western culture and believed the US operated a cell of spies in Benghazi.

Prosecutors allege that he directed the attack by some 20 men armed with grenades and heavy weapons on the US consulate and a second annex building where agents of the CIA worked.

The attack set fire to the consulate, where Stevens and a second State Department official, Sean Smith, died of asphyxiation.

Later that night two former Navy Seals who were contracted to the consulate operation, Glen Doherty and Tyrone Woods, were killed by mortar fire on the annex.

The attack shocked the United States. Stevens was the first American ambassador killed in the field since 1979.

Republicans in Congress launched an intense investigation that accused president Barack Obama and then-secretary of state Hillary Clinton of mismanagement, neglect and covering up the truth of the incident.

- Murder and terror charges -

Khattala is facing 18 separate charges including murder and material support for terrorists.

The 12-person jury is to begin weighing a verdict after final arguments in the case wind up on Thursday.

Khattala's lawyers argue that although he is a conservative Muslim, he did not hate the West. To the contrary, they said he was a "Libyan patriot" who says he worked with Americans to bring down the Libyan dictator Moamer Kadhafi, who was killed in 2011.

The photographs and videos that show him at the site during the attack do not prove he was part of it, his lawyers say. He was only a bystander who came to watch.

But the US government argues he commanded the Islamist militia Ansar al-Sharia behind the attack.

Even if he did not physically participate, DiLorenzo argued, in a conspiracy "the defendant is equally liable."

- Test case -

Khattala's trial is a test case for foreign suspects forcibly brought to the United States for trial.

He was captured in 2014 when US special forces carried out a raid based on intelligence provided by a Libyan man who ultimately received a $7 million reward from the US government.

On November 4 a second Libyan accused of involvement in the Benghazi attack, Mustafa al-Imam, was put on trial in the same Washington court, days after being captured and brought to the United States.

Al-Imam was called one of the men who attacked the consulate.

Source: AFP