Tensions between police and protesters have flared again in the French capital after a police investigation concluded there was insufficient evidence to show that the assault on a young black man by an officer using a truncheon was a rape.

The conclusion on Thursday came a week after the arrest in the northern Paris suburb of Aulnay-sous-Bois of the 22-year-old victim, who has been identified only as Theo.

The 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.

However, an investigating magistrate had charged one of the police officers with rape and three others with aggravated assault and is still examining the case.

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

Protesters planned to gather on Saturday in front of the Bobigny court, which is where a judge will decide on February 20 whether the accused policemen will face trial.

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.

'Police harass us'

Fury over the incident has culminated in days of peaceful protests and riots, with fireworks thrown at police as cars and rubbish bins were set on fire leading to dozens of arrests.

Theo, who said that police raped him with a baton, called for calm while being treated. Francois Hollande, the French president, visited him in hospital.

Bruno Le Roux, interior minister, said on Friday that police equipped with body cameras would patrol "sensitive areas" to film arrests and searches.

Yasser Louati, a French human rights and civil liberties activist, told Al Jazeera: "The police is now seen as an occupying force, not a force of protection for the weak and against crime.

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"There is an atmosphere of open defiance to the state ... the fear is that this might spark riots before the election, [which] may be a blessing for the right and far right."

Dorian Chacon, a football coach who lives in Aulnay-sous-Bois, told Al Jazeera: "They're supposed to protect us. They don't, they harass us. We don't feel safe here. They claim this is an accident: they take us for idiots. It's a total lack of respect."

Billel Kerzazi, Theo's friend, told Al Jazeera: "It's someone we know, so it's painful to think of what happened to him."

Rezmond Bukri, who also lives in the suburb, said: "The police are denying it, but they have to take responsibility, it's not right."

Police union viewpoint

The case has revived the contentious issue of policing in France's deprived suburbs.

In an interview with the Associated Press news agency, Yves Lefebvre, a police union chief, suggested the rape charge was filed "to calm or to stop a violent outburst" in what is a sensitive suburban neighbourhood.

Aulnay-sous-Bois was one of the worst-hit suburbs during 2005 riots around Paris.

Lefebvre said there was no evidence so far that "the truncheon was actually introduced" into the victim's rectum. And if that actually happened, it was likely done "accidentally", he said.

Defender of Human Rights, an independent French watchdog group, has said it will investigate "this dramatic case that illustrates the conflicts that sometimes arise from identity checks".