Telesforo Santiago Enriquez, who founded a community radio station in an indigenous region in southern Mexico was shot dead, the fourth reporter murdered in the country this year.
Mexico began investigating the murder of another journalist as the industry observed World Press Freedom Day on Friday, the latest casualty in one of the world's most dangerous countries for media workers.
Telesforo Santiago Enriquez, a retired teacher and founder of a community radio station, was found shot to death in a car on Thursday in the southern state of Oaxaca, the state prosecutor's office said in a statement later that day, adding that it had launched a probe into the killing.
Enriquez is at least the seventh media member to be killed during President Andres Manuel Lopez Obrador's administration. In March, deputy interior minister for human rights Alejandro Encinas, said six others had been murdered since Lopez Obrador took office in December.
Jesus Ramirez, a presidential spokesman, said the government would work to bring the killer to justice. Human rights organizations have criticized the government for not doing more to put an end to a long series of attacks on journalists and punish the people responsible for them.
"We are committed to finding those responsible for attacks against Mexican journalism," Ramirez wrote in a post on Twitter.
Encinas has said the government would seek more funding for a program geared to protecting journalists, without specifying the amount.
"On the radio waves, Santiago Enriquez expressed his analysis and criticism of the government and recently publicly denounced the municipal authorities for alleged diversion of resources," the National Human Rights Commission, Mexico's ombudsman's office, said in a statement.
Dangerous beat for journalists
Mexico is one of the most dangerous countries in the world for journalists. At least 124 media workers killed since 2000, according to rights group Article 19.
Watchdog group Reporters Without Borders ranks the country as the third-most-dangerous in the world for the press, after war-torn Afghanistan and Syria.
"This latest murder is a reminder of how dangerous it is to practice journalism in Mexico," the group's Latin America director, Emmanuel Colombie, said in a statement.
Santiago Enriquez's niece, Aida Valencia, said she believed her uncle was killed in retaliation for his work as a journalist.
"They shot him in the mouth and heart," she said.
Santiago Enriquez was also a school teacher, and was known for his work to preserve the region's indigenous languages and traditions, she said.