SAO PAULO (AP) — Current and former police officers may have committed up to 30 murders during the recently ended police strike in Brazil's northeastern state of Bahia, law enforcement officials there said.

Up to 30 people were killed execution-style out of the 180 murdered during violence that hit the state during the 12-day strike, said Arthur Gallas, head of the police department's homicide department, during a late Monday briefing for reporters.

The victims' bodies were found with their hands cuffed or tied behind their backs, he said. All of them had been shot in the head at close range with heavy caliber weapons such as the rifles Brazil's police carry.

"Preliminary investigations and eyewitness reports lead us to believe that these killings were the work of militias," Gallas said.

Prevalent in many Brazilian cities, such militias are paramilitary criminal organizations made up of former or active-duty officers that dominate poor areas, extort residents and often double as extermination squads, according to legislative and judicial investigations.

Investigators said it appears the militias took advantage of the strike to execute people who had been causing trouble in the areas they control.

"The crimes suspected of involving police officers are characteristic of groups that provide clandestine security services to storeowners in low-income areas," Gallas said. "All of the victims were young drug users, black, with no known address and with police records involving theft and burglaries in areas where (the militias) circulated."

Gallas said "various" police or former police are suspects but he gave no indication exactly of how many may be involved in the killings. He emphasized that as yet, nobody has been charged. But he said a rigorous investigation is being conducted and will continue.

He did say that solving the crimes will be difficult because police who may not be involved but have knowledge of the killings are unlikely to talk.

According to Guaracy Mingardi, a crime and public safety expert and researcher at Brazil's top think tank Fundacao Getulio Vargas, killings by police can be attributed to the "character of each individual and to internal issues like the fact that in many cities police are encouraged by their officers to kill."

Throughout the 1990s, policing policies openly gave officers in some Brazilian cities promotions and cash bonuses for engaging alleged criminals in shootouts that resulted in death.

During the recent work stoppage by some 10,000 of Bahia's 32,000 police officers, the state saw the homicide rate double in and near the capital city of Salvador, where Gallas said most of the apparent militia killings occurred.

Order was restored after 3,600 soldiers and federal police began patrolling the metropolitan area and regions around the state.

The strike ended Saturday when police unions agreed to a 6.5 percent pay raise, rights to some bonus payments and amnesty from punishment for striking officers as long as they didn't commit any crimes during the stoppage.

Two days later, police in Rio de Janeiro ended the strike they had begun late Thursday despite a state legislature vote giving officers a 39 percent raise staggered over this year and the next. The strike didn't affect Rio's security situation, and the government made no new concessions to officers.

The two strikes and the threat of similar action in other Brazilian states stoked concerns about Brazil's security forces ahead of its hosting of the 2014 soccer World Cup and the 2016 Olympics.