LE BLANC-MESNIL, France, Nov. 5 -- Mohammed Rezzoug, caretaker of the municipal gymnasium and soccer field, knows far more about the youths hurling firebombs and torching cars on the streets of this Paris suburb than do the police officers and French intelligence agents struggling to nail the culprits. He can identify most of the perpetrators. So can almost everyone else in the neighborhoods that have been attacked. "They're my kids," said Rezzoug, a garrulous 45-year-old with thinning black hair and skin the color of a walnut. While French politicians say the violence now circling and even entering the capital of...