Gunmen killed at least 18 people in outlying districts of Brazil's largest city, Sao Paulo, in a series of overnight attacks Aug. 14. Witnesses and video footage in several locations indicated that masked gunmen pulled up in a car before opening fire. In many cases they checked the victims' names before shooting, or asked if they had criminal records. At least six other people were injured in the attacks, in the districts of Osasco and Barueri. Authorities are said to be investigating whether the attacks were a coordinated campaign of revenge by off-duty officers following the deaths of two colleagues in the targeted districts the previous week. Police in Brazil are responsible for more than 2,000 deaths per year, and off-duty officers rarely face prosecution for vigilante justice. (Reuters, BBC News, Aug. 15)

Two days after the killings, Brazilians took to the streets across the country for protests against President Dilma Rousseff, whose administration is being shaken by corruption scandals amid growing economic agony. (AP, Aug. 16)