The Brazilian government has sent investigators to the south-eastern state of Minas Gerais to look into the murder of journalist Evany Jose Metzker.
Mr Metzker's body was found on Monday in a rural area near the town of Padre Paraiso, five days after went missing.
He had been tortured and decapitated.
Colleagues said Mr Metzker, 67, had been investigating drug trafficking and child abuse in the Jequitinhonha Valley region, one of Brazil's poorest areas.
Local journalists said they were afraid to work in the region.
"There is a climate of terror in the region that intimidates reporters from doing their job," the president of the Minas Gerais journalists' union, Kerison Lopes, said.
Mr Lopes told Spanish news agency Efe that "everything led them to believe that Mr Metzker was killed because he was reporting on robbery, drug trafficking and the sexual exploitation of children and adolescents".
He said the brutality of the murder had thrown local journalists in the region into panic.
According to the New York-based Committee to Protect Journalists, at least 14 Brazilian journalists have been killed since 2011 over their work.
However, a local police officer said they were not ruling out the murder could have been "a crime of passion".