El Debate reports that Gregorio Rodriguez Hernandez was eating with his family at a restaurant and was shot point blank in the head and chest, according to bystanders.
Rodríguez covered different local beats, including sports, society and crime.
El Debate news editor Juan Carlos Ramírez said the killing could have had something to do with a brief story published on November 24 about a physical attack by two suspected drug traffickers on a doctor who refused to treat an injured person. But Ramirez also said it was possible the killers mistook Rodriguez for someone else.
Reporters Without Borders, an international press freedom group, condemned the slaying.
"In view of the increasing violence in Mexico, especially against the press, all aspects of this murder must be investigated thoroughly, including the possibility that it was linked to the victim's work as a journalist," the organization said in a letter to Sinaloa governor Juan S. Millan.