An unidentified gunman killed Coelho, administrative editor and publisher of the local thrice-monthly newspaper A Verdade, outside his house with a .45-caliber handgun.
The journalist was murdered just one day before he was scheduled to testify in a criminal defamation lawsuit.
Some local observers claimed that Coelho had persuaded local politicians to bankroll A Verdade in exchange for favorable coverage, according to the Brazilian media news Web site Comunique-se.com. Conversely, other sources claimed that Coelho had used the threat of negative coverage to extort money from politicians.
The suit against Coelho was brought by Magé mayor Narriman Zito and her husband, José Camilo Zito dos Santos, mayor of the local municipality of Duque de Caxias, after A Verdade printed the minutes of a state legislative assembly session during which a political rival of Narriman accused her of having an affair with one of her security guards.
A Verdade often criticized local politicians for alleged corruption, and Coelho's father told the Brazilian daily O Globo that his son had received several phone threats five months before his death.
On September 14, acting on an anonymous tip, Magé police arrested retired Military Police sergeant Manoel Daniel de Abreu Filho as a suspect in the murder, according to O Globo. The person who tipped off the police also told them that de Abreu Filho had worked as a security guard for Rio de Janeiro state assemblywoman Andréia Zito, daughter of Duque de Caxias mayor Zito dos Santos.
At the time of his arrest, de Abreu Filho worked as a bodyguard for the wife of Waldir Zito, mayor of the city of Belford Roxo and brother of José Camilo Zito dos Santos.
After witnesses were shown a picture of de Abreu Filho and recognized him as the murderer, Judge Geraldo José Machado ordered that he be held in temporary prison. The police seized two handguns from de Abreu Filho and will perform ballistic tests to determine if they were used in the crime. The police are also seeking to determine whether de Abreu Filho acted on his own or followed orders.