Dozens of people have been killed in Rio de Janeiro, Brazil's second largest city, in a massive week-long crackdown on drug gangs. Authorities say the violence started when jailed gang leaders ordered their followers to attack police stations. But it could also be part of major clean-up operation as Brazil prepares to host the 2014 Fifa World Cup and the 2016 Olympics. Can the government win this battle and how powerful are these gangs?
