The main suspect in the trial of alleged accomplices in the 2015 Paris terror attacks caused an uproar in court Friday when he threatened a policewoman during her testimony.

"You will pay for this," shouted Ali Riza Polat, who 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 threat came as the witness, a policewoman working in an anti-terror unit, gave the court her account of Polat's conversion to radical Islamism.

She 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, the police agent said, told the friend that Polat had called her an "unbeliever" and "perverse".

From behind the glass screen of the defendants' box, Polat 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".

Polat's lawyer, Isabelle Coutant-Peyre, acknowledged that her client, who has gained a reputation as a hothead during the trial, "sometimes loses his cool" but said his reactions were those of "somebody who believes he is being accused unfairly".

Polat, she said, had specifically responded to the part of the testimony about his relationship with his mother.

Police have carried out constant patrols at the Paris courthouse since the Charlie Hebdo trial opened in September. Police have carried out constant patrols at the Paris courthouse since the Charlie Hebdo trial opened in September. Photo: AFP / Thomas COEX

"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."

Polat, 35, is facing the most serious charge of the 14 suspected accomplices on trial, complicity in terrorist crimes, and could face life in jail if convicted.

Born in Istanbul, Polat moved to France when he was three and said he fell into petty crime when he was 13 or 14, later starting to deal drugs. He grew up in the same rough Paris suburb of Grigny as Amedy Coulibaly.

Polat and the other suspects went on trial on September 2, accused of having helped the killers of 12 people in the attack on satirical weekly Charlie Hebdo, of a female police officer a day later, and of four men in a hostage taking at a Jewish supermarket.

All the attackers were shot dead by police.

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