Prosecutors and defense lawyers have given starkly different portrayals of Ahmed Abu Khattala, the alleged mastermind of the 2012 attacks on US outposts in Benghazi, Libya, that killed ambassador Chris Stevens and three other Americans.

Khatallah has been awaiting trial since 2014, when he was captured by a team of US military and FBI officials in Libya and transported on a 13-day journey to the United States aboard a navy vessel.

A government lawyer said on Monday that when Abu Khattala’s hatred of America boiled over, he orchestrated the attacks and then triumphantly strode around the attack site carrying an AK-47. The assistant US attorney John Crabb said that later, the defendant was heard at his apartment saying: “I attacked the American embassy” and would have killed more Americans that night if others had not intervened.

US consulate attack in Benghazi: a challenge to official version of events Read more

A defense attorney, on the other hand, called Abu Khattala a “Libyan patriot”, who fought on the US side in the war against the Libyan leader Muammar Gaddafi. He said Abu Khattala did not mastermind the attack. The lawyer said the defendant simply went to the attack site because he heard there was a protest and wanted to see what was happening.

“He didn’t shoot anyone. He didn’t set any fires. He did not participate in the attacks,” said Jeffrey Robinson, a lawyer for Abu Khattala.

Twelve jurors and three alternates listened as opening statements unfolded in one of the most significant terrorism prosecutions in recent years. The trial is being held in US district court in Washington – a civilian federal court – at a time when the Trump administration has said terror suspects are better sent to the military prison at Guantánamo Bay, Cuba.

The Benghazi attack led to a political firestorm in Washington, where Republicans repeatedly accused the then secretary of state, Hillary Clinton, of failing to adequately protect the diplomatic compound.

Abu Khattala, sporting a long grayish-white beard, appeared in court wearing a white shirt and dark pants. He has pleaded not guilty to the charges, including murder of an internationally protected person, providing material support to terrorists and destroying US property while causing death. When he entered the courtroom, he shook hands with members of his legal team. He monitored his trial with earphones offering him an Arabic interpreter. At times, he sipped water or swiveled in his chair at the defense table.

An 18-count indictment against Abu Khattala arises from a burst of violence that began on the night of 11 September 2012, at a state department compound, a rampage prosecutors say was aimed at killing American personnel and plundering maps, documents and other property from the post.

Facebook Twitter Pinterest A man surveys the damage inside the burnt US consulate building in Benghazi on 13 September 2012. Photograph: Gianluigi Guercia/AFP/Getty Images

Stevens was killed in the first attack at the US mission, along with Sean Patrick Smith, a state department information management officer. Nearly eight hours later at a CIA complex nearby, two more Americans, the contract security officers Tyrone Woods and Glen Doherty, died in a mortar attack.

Stevens and Smith “choked to death by thick black smoke”, Crabb said. Woods and Doherty were “blown apart by mortar”, he said. He said Abu Khattala “hates America with a vengeance” and that his “hatred simmered until it boiled over”.

“He killed Ambassador Stevens – a man of peace.”

Crabb said the prosecution would show the jury videos of the attack site and Abu Khattala’s phone records, which he said showed a spike in activity during the attacks. He said witnesses would include weapons and fire experts and a man named Ali, who was paid $7m to befriend Abu Khattala and help US forces capture him in Libya.

After he was captured, he was taken to a US navy ship that transported him to the United States. During the voyage, he was first interrogated by intelligence personnel and then by FBI agents. Crabb said Abu Khattala had told FBI agents that America was the “root of all the world’s problems”.

Robinson said Abu Khattala cooperated aboard the ship and he “continued to deny, as he denies today, any participation in planning or masterminding the attack”. He alleged that the witness was one of Abu Khattala’s adversaries in Libya who would do anything to have him locked in prison.

Robinson also said Abu Khattala was a deeply religious man who believed in conservative sharia law as outlined in the Qur’an, but reminded jurors that in America, people are not prosecuted because of their religious beliefs.

The trial, which is expected to last for weeks, is likely to resurrect the political controversy over the attack. Republicans accused the Obama administration of intentionally misleading the public about what transpired at the US outposts and stonewalling congressional investigators.