"We had never seen anything like this before," the criminal investigator told the Palace of Justice in Paris on Friday.

"Dried blood, shattered teeth, vibrating mobile phones, dead bodies, dead bodies, dead bodies."

The attackers, two of whom blew themselves up, were hard to identify at first glance, he said, as were several of the victims.

At times, the official struggled for words and to compose himself when describing the scene that the forensic investigators discovered in the Bataclan in the immediate aftermath of the attacks.

"I want you all to understand what it means to shoot with a 7.62 calibre, they don't just have an entry point and an exit point," he said, adding that the victims, who were shot at close range, were unrecognisable.

"I had the impression of an execution, one by one," the officer said when describing the bodies he found at the bar.

In the process, the terrorists shouted at their victims, justifying their attack, the officer said.

"Why are we doing this? You are bombing our brothers in Syria and Iraq and we have come here to do the same," one of the three yelled.

Police analysed an audio recording of the entire attack, until emergency crews intervened.

US and French citizens kill women and children in Muslim countries, the militants shouted.

"Now is the hour of retribution."

The first 22 seconds of the recording were played in the courtroom.

At the start, the concern can be heard, before shooting starts.

In the series of attacks on November 13, 2015, extremists killed a total of 130 people and injured 350 others by carrying out a massacre at the Bataclan concert hall before shooting randomly into nearby bars and restaurants.

Elsewhere, three suicide bombers blew themselves up at the Stade de France during an international football match between Germany and France.

Twenty suspects are currently on trial, with the majority of the defendants facing 20 or more years in prison if found guilty.

Australian Associated Press