SAO PAULO: Police in Brazil's northern city of Manaus say they are investigating if death squads formed by police officers or drug gangs were behind the weekend killings of 35 people. The killings began Friday night after a police officer was shot dead outside a bank. The killings occurred over the next two days in different parts of the city. Orlando Amaral of the Manaus civil police said Tuesday that they are investigating whether the killings could have been committed by police officers as an act of reprisal for the murder of their colleague, or resulted from fighting among drug gangs. Manaus will host football matches during the 2016 Olympic Games.