Shootings in Brazil's biggest city, Sao Paulo, left at least 19 people dead and seven others injured on Friday, security officials said.
Alexandre de Moraes, head of the Sao Paulo State Public Safety Department, spoke at a news conference saying that police are trying to determine if the shootings in the western suburbs of Osasco, Barueri and Itapevi on the western outskirts of Sao Paulo had a connection with each other, adding that the number of deaths is still considered preliminary.
Moraes said 15 of the victims were shot dead in Osasco, three were killed in Barueri and one in Itapevi, while the seven injured victims were treated at hospitals.
"We will investigate if the killings were committed by drug traffickers, by off-duty police officers or were acts of vengeance for the recent killings of two police officers,” Moraes said.
Amnesty International said in a statement that the killings were a "massacre.”
“Unfortunately massacres like this one in Sao Paulo have become part of the routine of violence in our cities,” said Atila Roque, head of the organisation's Brazil branch.
"Off- and on-duty policemen are frequently responsible for a significant portion of these homicides. A swift, impartial and transparent investigation must be conducted to discover who is responsible for this barbaric act,” Roque added.
Camera footage shows a group of identified perpetrators entering a bar and ordering clients to raise their hands in the air before shooting them.
Jorge Lapas, the mayor of Osasco, told the Globo TV network the killings may have been a quittance for the recent shooting deaths of two police officers.