French police placed four people four youths under investigation in connection with a bus attack Saturday in Marseille that left a passenger in critical condition.
Under the French legal system, being placed under investigation is one step short of the filing of formal charges
Officials say the teenagers, between the ages of 15 and 17, have previous records for delinquency.
A Marseille prosecutor, Jacques Baume, said three of the youths have admitted taking part in the incident.
The victim - a 26-year-old woman - remains hospitalized after being burned on more than half of her body.
The bus attack is one of the most severe incidents coinciding with the anniversary of riots that raged through mainly immigrant suburbs of France a year ago.
Immigrant families rioted last November to protest discrimination and a lack of jobs for young people.
Some information for this report was provided by AFP and AP.
