Last November a similar event in Litvinov, in the north, turned into a riot, with police fighting 500 right-wingers trying to get to a Roma neighbourhood blamed as ahotbedofcrime.
The attack comes as Rio, a former hotbedofcrime that had become safer in recent years, prepares to host next year's World Cup final and the 2016 Summer Olympics.
Much of her early career was spent as an assistant U.S. attorney, first in the Southern District, which includes Manhattan, and later in the Eastern District, home to Brooklyn and in the 1990s ahotbedof organized crime.