Luiz Felipe Muffo said on Thursday authorities are investigating whether the city's infamous First Capital Command gang was involved.

The First Capital Command gang reportedly controls most of the drug trade in Sao Paulo's slums.

It was blamed by authorities for a month of violence in 2006 that left 200 people dead, including police, prison guards, suspected criminals, jail inmates and bystanders.

Raids in slums of the Brazilian city of Rio de Janeiro are common but violence in Sao Paulo's slums is relatively rare.