Heber Lopez Vazquez, a reporter for the Noticias Web news site, was killed in the state of Oaxaca while he was inside his vehicle, said state prosecutor Arturo Calvo.
"We already have two arrests, we also have the weapons with which they committed the crime," the prosecutor said.
"Even if we have the two performers, we are not ruling out any leads that could lead us to the sponsors," added Mr. Calvo.
This is the fifth journalist murdered in Mexico since the beginning of the year, according to an AFP count based on data from Reporters Without Borders (RSF).
Mexico is considered one of the most dangerous countries in the world for journalists, exposed to reprisals from drug cartels operating in several of the country's 32 states.
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