BRASILIA

Civil police in Brazil's most populous state are investigating the possible involvement of military police officers in the killing of 12 people that occurred a few hours apart on Sunday night and Monday morning.

Civil police told local media that the homicides, which all took place in the same neighborhood of Campinas, in São Paulo state, appeared to be execution-style killings. The 12 men were shot hours after an off-duty military police officer was killed during an attempted robbery in the same area.

Civil police told local media they also had not ruled out the possibility of gang fight between local criminal groups.

"We have not ruled out execution, revenge or conflict between criminals," Civil Police delegate Licurgo Costa Nunes told Estadão do São Paulo daily newspaper. 

"It's a sequence of events in the same region, with times of occurrences close together, so we have to consider the relationship between them."

The Brazilian newspapers reported that half of those killed had police records, including for drug trafficking, murder and robbery.

Estadão reported that the sister of one of the victims had seen her brother’s killers in two cars, one silver-colored and one black. Witnesses at the sites of two other killings saw the same vehicles.

Later Monday morning, three buses in the region were set alight, and seven more were vandalized, apparently in response to the 12 killings. No one was injured in the bus attacks.

A spokesperson for the military police of Sao Paulo state could not be reached.

Military police in Brazil, and particularly in Sao Paulo, have been accused many times in recent years of using unlawful force and carrying out extrajudicial killings.

A 2013 annual security report produced by Brazil's Forum of Public Security and US non-governmental organization Open Society Foundations found that in 2012, police killed 1,890 people in 23 Brazilian states, averaging five murders per day.

In July, Human Rights Watch wrote to São Paulo Governor Geraldo Alckmin and State Attorney General Márcio Fernando Elias Rosa to urge them to conduct impartial investigations into alleged killings by police and ensure that officers who use unlawful force are held accountable.

 "Evidence gathered across cases in São Paulo shows a clear pattern of police executing victims and then covering up their crimes," said José Miguel Vivanco, Americas director at Human Rights Watch. 

"One of the most effective ways to stop these heinous crimes is to hold the police who commit them accountable, which will send a clear message that the police can’t execute people and get away with it."

In late 2012 there was a wave of violent crime in São Paulo that some analysts surmised was in retaliation to increased police brutality and killings.

In a 2009 report, Human Rights Watch documented cases where police officers misreported apparent executions, telling senior officers that the victims had resisted arrest and died during shootouts.

Other tricks to conceal extrajudicial killings included taking a victim’s body to the hospital, and claiming that they police had tried to rescue it from a violent incident.

By Lucy Jordan - Anadolu Agency