Beaumont-sur-Oise – Violence erupted on Thursday in the northern suburbs of Paris for a third night in a row, with 15 cars set ablaze by residents furious over the death of a young man in police custody.The unrest began on Tuesday night after it emerged that Adama Traoré, 24, had died shortly after being arrested in the town of Beaumont-sur-Oise.Authorities said an autopsy revealed he was suffering from a serious infection at the time of his death and that his body showed few signs of violence. He was taken into custody after interfering in the arrest of his brother in an extortion case, said a source close to the investigation.Local prosecutor Yves Jannier said Traoré "fainted during the ride" to the police station, and paramedics were called immediately but were unable to revive him.Jannier said the infection was "very serious" and had "impacted several organs", while the medical examiner had found scratches but no "marks of significant violence" on the man's body.However, Traoré's family said it would seek an outside expert's opinion before his burial. "The infection that Adama Traoré may have been suffering from does not explain the causes of his death," said the family's lawyer Karim Achoui.Traoré's twin sister, Hawa, said she did not believe the autopsy findings were accurate, but called for calm. "We will find the truth. Calm down," she told AFP, addressing those on the streets in support of her brother.'Healthy, tall, sporty guy'On Tuesday night five members of the paramilitary police were injured in clashes, and nine cars set on fire, while several public buildings were damaged. One person was arrested.The unrest continued on Wednesday night in a series of villages situated near each other some 30km north of Paris, where 15 cars were set ablaze and protesters tried to set a mayor's office and a pre-school on fire."Eight people were arrested. Some for throwing incendiary devices at security forces, others for trying to set a public building on fire," said local government official Jean-Simon Merandat.Youths in the suburb say they are convinced that police are responsible for Adama's death."He was healthy, a tall, sporty, stocky guy," said Sofiane, 30."We know it is going to be covered up. We know if things don't burn nothing will come of it, that is how we feel," said Ornel, 24.The violence comes as security forces are stretched to their limit, after months on high alert for terror attacks, and violent anti-government protests in which police have become a target of hatred.In 2005, two teenagers were electrocuted after hiding in an electricity substation while being chased by police, sparking weeks of massive riots.The violence was seen as an urban revolt against the system from France's "ghettos" with their grim high-rise buildings, high levels of poverty and unemployment and populations of first and second generation immigrants who feel marginalised by society.