World's most dangerous gangs

Primeiro Comando da Capital (PCC), Brazil:
... On Friday, May 12, the city of São Paulo came under siege as anonymous attackers burned buses, banks, and public buildings, gunning down police and instilling chaos as they went. Simultaneously, 73 prisons around the state erupted in rebellion. For days, the city and the prisons were at a standstill while local leaders floundered, unsure how to respond.