A five-hour killing rampage in Brazil’s southeastern city of Campinas has left 12 people dead.
The victims were gunned down in several separate incidents on the outskirts of the city, in what Brazilian media said appeared to be execution-style killings.
Authorities say they are looking into all possibilities, including whether the killings were gang-related.
But they also say the timing and location of the shootings add weight to a theory that they were revenge killings carried out by the police.
The slayings occurred between Sunday night and Monday morning, just hours after an off-duty military police officer, Arides Luiz dos Santos, was killed in an attempted robbery at a gas station.
According to Brazilian media, in one of the cases, a car pulled up, its occupants told children to go inside and then opened fire.
Hundreds of angry residents took to the streets to protest the killings. They attacked buses, burning three of them.
Police have stepped up their presence in Campinas, located about 50 miles northwest of Sao Paulo, to prevent further violence.
The latest deadly incidents come as Brazil prepares to host the 2014 World Cup in June.
None of the venues for the soccer tournament is in Campinas. However, fans from around the world are expected to flock to nearby Sao Paulo, the country’s financial and business hub.