"It is not because there are a few radicalised people (...) who tarnish the image of Islam that we are going to give in to the temptation to lump together all those who have chosen France", says the first secretary of France's Socialist Party, Olivier Faure, at the start of a demonstration in Paris against an immigration law. French prosecutors have opened an investigation into a "terrorist plot" after a man known to the authorities as a radical Islamist with mental health troubles stabbed a tourist to death and wounded two other people in a knife and hammer attack before being arrested. SOUNDBITES