The 25-year-old man died of a heart attack on Tuesday during a police check on a group of youths in a housing estate in the Paris suburbs, Le Parisien reports. The police was taking the man in for question when he collapsed and fainted.
Rescue workers did not manage resuscitate the man, whose family wants to keep him anonymous.
Local authorities say the police were searching the youths for drugs and did not use violence. They say the young man suffered from health problems and had gone into hospital for a cardiac test on Tuesday.
The autopsy shows that the man did not suffer from any blows and had died from a ruptured aorta. French prosecutors have however opened an investigation into his death.
Tensions have been high in Aulnay-sous-Bois since the death of the young man. Four youths were arrested overnight on Wednesday for throwing firecrackers and burning bins.
Riot police were deployed to prevent violence from spreading.
In 2005, the death of two teenagers of African origin sparked riots in Aulnay-sous-Bois.