A peaceful rally in a Paris suburb has descended into violence amid anger over the case of a black youth worker who was allegedly raped with a police baton.

Police on Saturday fired tear gas at protesters who threw projectiles at officers and set cars and rubbish bins alight.

More than 2,000 people gathered peacefully in the northern suburb of Bobigny outside the courthouse calling for justice for the 22-year-old victim, who has been identified only as Theo.

Later, however, some in the crowd hurled crude projectiles at riot police.

Al Jazeera's David Chater, reporting from Bobigny, said: "The whole area where the demonstration started is now soaking in tear gas."

He said the protesters were taking out their anger and frustration "over what they see as a burning sense of injustice" out on the streets.

A police statement said: "Several vehicles, including a media truck, were set on fire and police officers had to intervene to rescue a young child trapped in a burning vehicle."

Fury over incident

On February 20, the Bobigny court will decide whether the accused policemen - who all deny the accusations against them - will face trial.

"Instead of being a peaceful demonstration trying to get justice outside the courthouse where we will hear what will happen to those police officers," our correspondent said, "this has turned into a series of running fights, in what I'm hearing will continue into the night."

Saturday's riots came more than a week after one of the accused policeman was placed under formal investigation for suspected rape and three others for unnecessary violence during Theo's arrest in Aulnay-sous-Bois, a northern suburb of Paris.

READ MORE: Paris police say rape of black man an 'accident'

Fury over the incident has culminated in days of peaceful protests and riots.

On Friday, AFP news agency cited a police source as saying that having taken into account CCTV recordings and witness accounts, "there are insufficient elements to show that this was a rape".

A video of the scene shows a policeman "applying a truncheon blow horizontally across the buttocks with a truncheon" and Theo's trousers "slipped down on their own", the source said.

A lawyer for the officer charged with rape said that any injury inflicted was done accidentally.

Video that apparently showed Theo's arrest circulated on the internet, showing the youth worker on the ground against a wall being beaten by four men.

Theo, whose family say he was not known to police, required surgery for severe anal injuries after he was assaulted with a truncheon, and also suffered head trauma.

Yasser Louati, a French human rights and civil liberties activist, told Al Jazeera: "Police brutality is not a random and isolated event, but is more accurately a structural problem that [the government] has so far refused to address ... nobody wants to see what is happening at the systemic level."

READ MORE: Justice for Theo - Protests erupt after police rape

The solution, he said, does not lie in "cosmetic changes ... it is in addressing [the question] why do these events keep happening? Unless you address the why, these events will keep happening".

"My fear is that what's happening in Aulnay-sous-Bois might result in more riots, giving credit to Marine Le Pen or right-wing candidates."

Theo's suburb of Aulnay-sous-Bois was one of the worst-hit areas during 2005 riots around Paris, which were prompted by the deaths of two teenagers - Zyed Benna, 17, and Bouna Traore, 15 - who were electrocuted after running away from police.

That incident touched off three weeks of violence in which 10,000 cars and 300 buildings were set on fire, spurring Nicolas Sarkozy, then interior minister, to declare a state of emergency.