The killing of eight people by São Paulo police in the course of one night last weekend could point to a cycle of revenge killings between police and gang members, threatening the city’s recent security gains.

The killings took place in six separate incidents. In each case, police said that they were patrolling when they encountered a suspicious vehicle whose occupants refused to stop, resulting in a shootout, as Jornal Floripa reported. No police officers were reported wounded in any of these shootings. According to EFE, São Paulo’s Public Safety Secretariat said the killings took place when police responded to resistance by suspected criminals, and that an internal investigation was taking place.

The shootings came after a series of attacks in São Paulo in June, when seven officers were killed and five police stations attacked, as well as 15 city buses burned, suggesting that the weekend of police violence could have been retribution. One of the dead was suspected of recently shooting at a police station, which could explain why they were targeted.

There is reason to believe the First Capital Command (PCC) drug gang is responsible for at least some of the June killings, and that some of those shot by police were members. A report by Estadao said that a police intelligence recording showed an alleged PCC member giving instructions to “release the boys” on the police, and that residents of one São Paulo neighborhood said the bus burnings were a response to police brutality. The similar number in terms of those killed on each side also points to a revenge killing.

According to reports, the group had threatened to attack officers in retaliation for the May killings of six of its members in São Paulo. A prison inmate in Marilia, São Paulo state allegedly told a police officer that the PCC was preparing to kill around 60 civil and military police officers throughout the state earlier this month, reported Rede Bom Bia. The officer sent an e-mail to colleagues warning of the threat that closed with the following:

Let’s see if this email is true on July 9 (this Monday). For security reasons, as I confront the criminals of the PCC, I will send my family out of São Paulo. May God have mercy on all of us.

However, Jornal Floripa reported that police intelligence sources also suspect that rival drug trafficking organizations, or elements of the police themselves, could be behind the murders of officers in June.

It is worth noting that the PCC has already pulled off one large-scale massacre of police in São Paulo. In May 2006, members of the group killed more than 40 police officers and prison guards in a deftly coordinated rebellion in São Paulo’s prisons and streets, burning buses, throwing grenades from cars and roving the streets in armed bands. By the time the gunshots and explosions had quieted, more than 180 were dead, and violence had spread to a handful of other cities, evidence of the group’s presence across the country. During the clashes there were also mass killings of suspected gang members by police.

There are signs that the cycle of police abuse and retaliation is beginning to heat up. Lethal force by police has increased 5 percent so far this year, compared to the same period last year.

Another outbreak of murders would be all the more troubling because it would undermine São Paulo’s security gains over the last few years. The last time São Paulo was paralyzed by a PCC-police war, in 2006, the city had a murder rate of 25 per 100,000, according to a study (see pdf) by the São Paulo think tank Instituto Sangari. Now, the rate has fallen to less than 16.

Guaracy Mingardi, ex-director of the National Public Safety Secretariat, said, “it is difficult to say for sure what is currently happening. But what is clear is that police are killing more and this could indicate a lack of control inside the Military Police,” Jornal Floripa reported. The authorities should take a close look at the circumstances in which eight people lost their lives, and try to avoid kicking off a bloody cycle of revenge that could threaten the recent security gains in the city.