IN retrospect, it was not a good idea to have left his pistol at home. Called to the scene of a traffic accident in the Paris suburbs last Sunday, Jean-François Illy, a regional police chief, came face to face with a mob of immigrant youths armed with baseball bats, iron bars and shotguns.

What happened next has sickened the nation. As Illy tried to reassure the gang that there would be an investigation into the deaths of two teenagers whose motorbike had just collided with a police car, he heard a voice shouting: “Somebody must pay for this. Some pigs must die tonight!”

The 43-year-old commissaire realised it was time to leave, but that was not possible: they set his car ablaze. He stood as the mob closed in on him, parrying the first few baseball bat blows with his arms. An iron bar in the face knocked him down.

“I tried to roll myself into a ball on the ground,” said Illy from his hospital bed. He was breathing with difficulty because several of his ribs had been broken and one had punctured his lung.

His bruised and bloodied face signalled a worrying new level of barbarity in the mainly Muslim banlieues, where organised gangs of rioters used guns against police in a two-day rampage of looting and burning last week.

Not far from where Illy was lying was a policeman who lost his right eye after being hit by pellets from a shotgun. Another policeman displayed a hole the size of a 10p coin in his shoulder where a bullet had passed through his body armour.

Altogether 130 policemen were injured, dozens by shotgun pellets and shells packed with nails that were fired from a homemade bazooka. It prompted talk of urban “guerrilla warfare” being waged on French streets against the forces of law and order.

By the end of the week an extraordinarily heavy police presence in Villiers-le-Bel, where most of the rioting took place, appeared to have halted the violence: on top of public transport strikes and student protests against his reform plans, Nicolas Sarkozy, the French president, could not afford a repeat of 2005, when a similar incident involving the deaths of two youths provoked the worst French urban unrest in four decades.

Things were so tense in the suburbs, however, that the riots could easily erupt again with the prospect of deaths on either side setting off a much greater explosion and, conceivably, the deployment of the army to keep peace.

“Given the weapons being used, it was lucky that nobody was killed,” said a policeman. Nearby were the charred remains of the local constabulary. The nursery school was burnt down. So was the library.

Rioting two years ago was widely regarded as a protest against poor housing, racial discrimination and unemployment of up to 40% in the grim housing estates surrounding most big French cities.

But “Sarko” dismissed suggestions that nothing had been done to improve the situation, referring to the “Marshall plan” for the banlieues being drawn up by Fadela Amara, his urban development minister.

At the same time he argued that, far from reflecting difficult living conditions, the violence was a result of the “thugocracy” of the suburbs, where drug-trafficking criminals held sway.

“We shouldn’t try to excuse the inexcusable,” said the president in a television address to an anxious nation on Thursday, ridiculing the left’s vision of rioters as “victims of social injustice”. He pledged that those who fired at police would be tracked down, one by one, and tried on charges of attempted murder.

Lawlessness in the suburbs is an awkward issue for Sarkozy because he had promised to deal with it as interior minister, when he introduced “zero tolerance” policing, only to be accused of aggravating the problem by referring to trouble-makers as “thugs” and “scum”. Despite some successes, many of the suburban ghettoes remain a law unto their own and, like parts of New York in the bad old days, policemen do not like to set foot there.

“It felt like they were out to kill us,” said one of the officers in Villiers-le-Bel last week. “We knew that there were weapons in the suburbs, but they have never been turned against us like that. The kids were shooting at us at close range, loading and reloading their weapons. I’ve never seen anything like it.”

Sarkozy has ordered a full judicial inquiry into the teenagers’ deaths, even though all the evidence seems to support the police version that the boys were thrown from their unlicensed motorcycle when it accidentally collided with a patrol car. Friends and relatives of the victims dismiss the official account of the incident as fantasy.

As for Illy, he says he is not feeling vengeful but has identified one of his attackers from police photographs. He is certain to be able to pinpoint the rest. “Fortunately,” he said, “I’ve got a very good memory.”

Click here for a video of the Paris riots

Sarkozy pledges to punish rioters

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