Lopez Obrador was indignant about the "sad" of Fredid Roman, who was gunned down Monday night in Chilpancingo in the southwestern state of Guerrero.
Mexico's president on Tuesday deplored the killing of a journalist the day before, in a country where at least a dozen photographers or commentators denouncing collusion between elected officials and organized crime have been killed since the start of the year.
Andres Manuel López Obrador was indignant about the "sad" assassination by bullets of Fredid Roman Monday night in Chilpancingo, in the southwestern state of Guerrero.
"The day after tomorrow, we will have a report" on Roman's assassination, López Obrador promised during his daily press conference while presenting his condolences to the relatives.
The victim published a political editorial in a local newspaper, as well as a news page on Facebook.
A few hours before his murder, Mr Roman had published on the social network a text entitled "state crime without charging the leader".
He was going back to the recent government report calling the disappearance of the 43 students in Ayotzinapa (Guerrero) in September 2014 a "state crime".
In Mexico, journalism remains a risky business
Citing a "protected witness," Roman mentioned an alleged meeting between four officials at the time, including former Attorney General Jesus Murillo Karam, who has been in pretrial detention for "forced disappearance" since the report was released last week, and the former governor of Guerrero.
A few dozen people demonstrated with cries of "No to silence" on Tuesday in Acapulco, the tourist showcase of the state of Guerrero.
The local prosecutor's office said it was investigating whether Roman's murder was related to that of his son on 1 July.
Twelve journalists have been killed in Mexico since the beginning of the year, according to the government.
The journalists' rights organisation Reporters Without Borders (RSF) estimates that ten have been killed for their journalistic activities. Domestic media reports put the number of journalists killed in Mexico in 2022 at 15 to 16.
The victims are often journalists in a precarious situation who have to undertake other activities to earn a living. They may also be commentators on local politics who expose collusion between elected officials and organized crime from their own online publications.
Most murders of journalists go unpunished and occur in areas affected by drug trafficking.
"The collusion between the authorities and organized crime constitutes a serious threat to the safety of journalists," according to RSF.
"President López Obrador has still not undertaken the necessary reforms to curb this violence and the impunity that surrounds it," the NGO lamented.
With 150 journalists killed since 2000, according to RSF, Mexico is considered one of the most dangerous countries in peace for the press.