An arrest warrant was issued for Jorge Luiz Thais Martins, who commanded the state's firefighters' department from 2007-2009, for his alleged involvement in the killings that happened after his son's unsolved death in October 2009, according to the Parana state public safety department.
"Police are investigating the possibility the crimes were committed as vengeance," said Giovani Santos, a spokesman for the public safety department.
He said Martins is being investigated in part because a drug user who survived a recent attempted killing identified Martins as the shooter.
Martins could not be found by police during a search at his house on Thursday. Authorities would not disclose if they found new evidence at his home.
The killings happened in the southern city of Curitiba, in the neighborhood where Martins' 26-year-old son was killed by robbers who wanted to steal his car while he returned from a party. His girlfriend also was shot, but survived.
No one was arrested for the son's killing, but an underage drug user who lived in the region was briefly detained at the time and released because police said there was not enough evidence to charge him.
It was not clear whether the drug users killed recently had any connection to the one detained by police at the time of the son's death.
The public safety department said Martins' suspected actions have nothing to do with the firefighters' department that he commanded.