Washington (CNN) Donning gray pants, an untucked white button-down shirt and long gray beard, Ahmed Abu Khatallah silently took notes and sipped water inside a packed Washington courtroom on Monday as prosecutors outlined a case that will attempt to paint him as the ringleader of the 2012 terrorist attack on the US mission in Benghazi, Libya that killed Ambassador Chris Stevens and three other Americans.

Abu Khatallah "didn't light the fires or fire the mortars, but is just as guilty" for planning the attack, setting it in motion and getting others "to do his dirty work," federal prosecutor John Crabb told jurors in his opening statement.

But the defense ardently refuted Crabb's claims that Abu Khatallah "hates Americans with a vengeance" and facilitated the attack that killed four Americans during its opening remarks on the first day of trial.

The evidence will show Abu Khatallah -- the only Benghazi suspect currently in US custody -- is not guilty and that he "was just someone who could be blamed," said defense attorney Jeffrey Robinson.

Abu Khatallah faces 18 charges related to the deadly violence that began on September 11, 2012, including the murder of an internationally protected person, providing material support to terrorists and destroying US property while causing death.

During the attack, assailants armed with automatic weapons and rocket-propelled grenades first blasted through the main diplomatic mission before setting it ablaze, according to 2014 court papers.

Stevens and State Department information officer Sean Smith died there. A coordinated mortar assault on a nearby annex killed security officers Tyrone Woods and Glen Doherty, both CIA contractors and former US Navy SEALs.

"Ambassador J. Christopher Stevens choked to death by thick black smoke. Sean Smith choked to death by thick black smoke. Glen Doherty and Tyrone Woods were 'blown apart by mortar fire,' " Crabb said while vividly describing the attack that took place more than five years ago.

"I knew we were under attack"

Special agent Scott Wickland, a regional officer with diplomatic security who was living at the mission, recalled the events of September 11, 2012 as the first witness to testify in the trial.

Wickland was visibly emotional as he described Stevens as "very personable" with a warm manner was "not normal" for an ambassador.

Around 9:45 p.m. on September 11, Wickland said he heard chanting down the street from the mission and then calls of "Allah Akbar."

As guards scrambled to put on their protective gear and get their guns, Wickland said went to notify Stevens -- who had already gone to bed -- of a possibly escalating security situation.

Wickland then said he directed Stevens and IT official Sean Smith to a safe room in one of the compound's villas.

There was gunfire, explosions and "bloodcurdling screams" on the radio, according to Wickland, who told the jury, "I knew we were under attack."

The doors of the villa were then blown open and attackers entered the compound armed with AK-47s and other assault rifles, he said.

When the attackers could not blast open the gates of the safe room, they set the villa on fire, Wickland said.

With smoke filling the safe room, Wickland told the jury that he tried to lead Stevens and Smith to the bathroom so they could get some air but quickly realized they were not behind him.

He tried to feel around and yell for them but he couldn't find them -- searching until he was out of air and almost collapsed.

As Wickland went outside to escape the smoke he said he was fired upon by grenades.

He repeatedly entered the compound to search for Stevens and Smith until he was out of breath only to be met with a barrage of grenade fire each time he exited the compound.

Unable to locate Stevens and Smith, Wickland told the jury that he said to himself "I'm going to search for them until I'm going to die."

Wickland then said he waited for a lull in the gunfire and climbed a ladder to the roof where he stayed alone for a very long time and continued to take fire -- unable to make contact with anyone on the radio.

Just when he thought everyone was dead, one of the special afents, David Ubben, called Wickland on the radio and said "are you alive?

"I don't know how many times I thought I was going to die, but this was a piece of hope that I was going to survive," Wickland told the jury.

Court adjourned for the day as Wickland was still on the stand and the prosecution is expected to resume his testimony on Tuesday.

Violent extremist or Libyan patriot?

Abu Khatallah emerged from years in prison under the regime of former Libyan leader Moammar Gadhafi to form an Islamist militia and later became associated with Ansar al-Sharia, a group US officials blamed for the 2012 attack.

Believed to be in his 40s, Abu Khatallah became the face of the militant attack and a top target for the US after he cultivated a celebrity profile in its wake, meeting with journalists and granting interviews.

On Monday, prosecutors highlighted evidence they said will show Abu Khatallah not only orchestrated efforts to gather weapons ahead of the attack but will also show he rushed the gates of the mission armed with an AK-47 rifle and fuel canisters which were used to set the building on fire.

The prosecution ended its opening statements by reiterating that Abu Khatallah was motivated by his hate for Americans and concerns that the US mission in Libya served as a "spy nest" -- a point that echoed claims made in pre-trial documents.

"The defendant's participation in the attack was motivated by his extremist ideology," prosecutors said in the documents, which also alleged that Abu Khatallah "voiced concern and opposition to the presence of an American facility in Benghazi" days prior to the attack.

However, the defense argued that Abu Khatallah was not a radical terrorist but rather a "Libyan patriot" who fought to free the country from Gadhafi.

According to Robinson, Khatallah was at a friend's house when he heard about the attack and "went to see what was going on."

He did not attempt to block people from going to the attack site but was only acting to try and protect those present from gunfire, Robinson said, adding that Abu Khatallah never went to the CIA annex and was at home when the mortars hit.

The defense also discussed Abu Khatallah's 12 days in isolation after he was captured during a secret raid in June 2014.

While he was interrogated aboard a Navy ship during transport from Libya to the US, the defense said Abu Khatallah made certain statements and blamed bad translation for his answers.

They also emphasized that he cooperated with interrogators without an attorney present.