In Brazil, four police officers have died after their helicopter crashed over Rio de Janeiro's notorious City of God favela. In dramatic footage of the crash, sustained gunfire can be heard before the helicopter drops from the sky like a stone, narrowly missing a main road. <br/><br/>According to police, the helicopter was giving support to a police operation against gangs in the favela. There had been several clashes during the day between police and criminal gangs operating in the area.<br/><br/>A police spokesman said that forensics officers were examining the wreckage to determine the cause of the crash. If the helicopter was shot down by gang members, it would not be a first for the city, which hosted the 2016 Olympics.