The French national is believed to have fought alongside ISIS in Syria in 2013. He is described by some witnesses as an admirer of Mohammed Merah, who committed the 2012 Jewish school shooting in Toulouse.
Mr Bendrer, who is suspected of providing the weapons for Mr Nemmouche’s own attack, was arrested seven months later in December 2014.
Both men say they are innocent.
In Belgium, all criminal trials begin with the prosecutor reading out the so-called Accusation Act, a document detailing the facts of the case and the charges.
On Thursday, two prosecutors started reading that 190-page document, a timeline of everything that has happened in the case since the killer entered the museum.
The gruesome details sent shivers through the room.
“The killer entered the museum quietly through the main door, standing just behind Miriam and Emmanuel Riva, who were looking at tourism brochures,” the prosecution said.
“They did not notice him standing right there and he shot the husband first and then his wife in the neck.
“The killer then advanced into the main entrance office. An employee, 26-year-old Alexandre Strens, was walking towards the entrance, intrigued by the noise.
“He then saw the killer and tried to close a door between them. The killer then shot him in the forehead, wounding him critically.”
The fourth victim was Dominique Sabrier, a 66-year-old French woman who volunteered at the museum.
The prosecutor said: “She saw the killer and tried to hide under a desk but he walked towards her and shot her multiple times with a hand gun first and then with his automatic rifle.
“The killer then gets calmly back out of the museum, walking by Emanuel and Miriam Riva’s bodies without looking at them.”
The attack lasted only 82 seconds. It was filmed by a security camera.
For several hours Mehdi Nemmouche watched prosecutors as they laid out their case, occasionally exchanging words with his lawyers.
Those lawyers are one of the reasons this court case is different from other terrorism trials.
Sebastien Courtoy and Henri Laquay chose an unusual strategy: accusing Israeli intelligence of carrying out the museum shooting and setting up Mehdi Nemmouche.
“Everyone knows Mrs Riva was an accountant for the Mossad,” Henri Laquay told the JC. “Our client is innocent.”
Asked why he thinks the Mossad would kill four civilians and how they did it, the lawyer would not answer.
“This is precisely what will be discussed and discovered during the trial, I can’t reveal it now. All I can say is that Mehdi Nemmouche did not fire these weapons. We have scientific evidence proving that.”
Asked whether Mr Nemmouche was in the museum that day, the lawyer replied: “No, he wasn’t.”
This unprecedented line of defence based on a conspiracy theory has shocked Belgium’s Jewish community.
“We’re concerned the defence, or the suspect, will try to minimise the antisemitic nature of this terrorist attack and use conspiracy theories,” Yohan Benizri, the leader of Jewish Belgian umbrella group CCOJB told the AFP news agency.
“These theories’ goal is to change the subject, not talk about what has happened.”
Mr Nemmouche’s lawyers have a history of controversial clients: they represented antisemitic comedian Dieudonné M’bala M’bala in the past.
Meanwhile the Jewish museum says it stands firm and continues its mission.
“Our message has been: no matter the horror of the attack, the terrorists have not destroyed us,” museum lawyer Adrien Masset told the JC.
“By attacking the museum they tried to attack history of humanity, our society’s multicultural heritage, philosophy and human thought. The terrorists will not undermine this. They have failed.”
The trial is expected to last seven weeks.
