Record reward offered for information on killings of 18 in Brazil

"We believe we can obtain important information. This is a valid way (to catch the perpetrators). It's important that civil society collaborate and we're sure we'll get that collaboration," Sao Paulo Public Safety Secretary Alexandre de Moraes said in a statement.

The attacks, which also left six people wounded, occurred in a matter of three hours between Thursday night and dawn Friday at 10 different points in Osasco and Barueri, neighboring cities in the Sao Paulo metropolitan area.

Authorities believe the homicides were committed by the same group, given that all occurred one after another within a 4-kilometer perimeter, and they also suspect, judging by the characteristics of the crimes, that the homicides could have been executed by members of the police force.

The crimes are under investigation by a special group made up of 70 police officers and detectives.

The reward will be awarded to the person who "can help police solve the crime by offering relevant information about the identity and whereabouts of the perpetrator," the Sao Paulo Public Safety Secretariat said.

"This is an absolutely secure reward program. Whoever offers worthwhile information will have his or her identity kept a total secret," Moraes said.

Investigators are considering the possibility that the multiple murders were acts of "revenge" by police for the slaying of two officers days before in the same area.

One factor that heightens suspicions about possible police involvement in the killings is that bullet shells found at the scenes of the slayings were of a kind reserved exclusively for use by police and the armed forces.

All the victims were men between ages 16 and 49, while six of them had criminal records for robbery, drug trafficking and attempted homicide.