Ramon Abel Lopez Aguilar, 53, was a photographer and editor of the news web site Tijuana Informativo.
His son-in-law, 22-year-old Raul Vazquez Hernandez, confessed to shooting Lopez Aguilar, Baja California state prosecutor Abel Galvan told a press conference in Tijuana.
Vazquez Hernandez said he shot his father-in-law twice in the head during a heated argument as they were sitting inside a vehicle, according to Galvan.
Both men had been drinking.
The shooter took Lopez Aguilar, who remained conscious, to a hospital, but left after doctors said they would have to inform police about the shooting.
The victim died minutes later and his son-in-law dumped the body on a street in Tijuana, later telling police that Lopez Aguilar had been kidnapped from his home by unknown assailants.