Twelve people were killed and 11 were injured when Saïd and Chérif Kouachi open fired at the Charlie Hebdo office in Paris on January 7, 2015.

Ali Riza Polet, who has been held as the attack’s mastermind and the only primary suspect held by the French authorities, caused an uproar in court Friday when he threatened a policewoman during her testimony.

Polet, who has been claiming his innocence since his arrest, shouted, “You will pay for this,” as a policewoman working in an anti-terror unit, gave the court her account of Polat’s conversion to radical Islamism.

Polet is believed to have been the right-hand man of Amedy Coulibaly, who killed a police officer in January 2015 and the next day shot dead four people at a Jewish supermarket, before being killed by police.

The policewoman said that Polat shared the religious convictions of his friend Amedy Coulibaly and recounted a conversation between Polat’s mother and a friend recorded in a wiretap.

“The mother told the friend that Polat had called her an unbeliever and perverse.”

As the witness completed her statement, Polat raised his voice from behind the glass screen of the defendants’ box. The accused had raised his fist several times, mimicking punches at the agent during her testimony, and was called to order by the court.

Chief prosecutor Jean-Michel Bourles, calling Polat’s outburst “a scandal,” said he would file criminal charges against him for “threats against a person testifying on behalf of the public authorities”.

On the other side Isabelle Coutant-Peyre, Polat’s defendent said, he had specifically responded to the part of the testimony about his relationship with his mother.

“She can lie about me, but not about my family,” Polat shouted, warning the officer that: “My brother-in-law is going to come.”

When the trial resumed after a lunch break, Polat apologised to the court and claimed he had not actually threatened the policewoman.

But the chief judge, Regis de Jorna, told him “you know very well what you’re doing and what you’re saying” and warned him: “If you ever threaten this investigator or anybody else again, you will be banned from the trial.”