Vigilante Miguel Ángel Jiménez Blanco who spearheaded the search for the 43 students who vanished last year in Mexico was found dead in his hometown of Xaltianguis. Investigators in Mexico's Guerrero state say Jiménez was killed inside a taxi he owned, with two gunshot wounds on Saturday 8 August.
Guerrero, which has one of the highest murder rates in Mexico, saw 1,514 murders in 2014 and 943 people who have been killed so far this year through June, according to federal statistics.
Police are treating the death of Blanco as murder, although they have not stated whether there are any suspects for the homicide.
The 45-year-old was a fierce critic of local officials who he claimed had hidden important evidence linkd to the students' disappearance.
Authorities say corrupt local police abducted the students and handed them over to a drug gang, who killed and burned their bodies.
Blanco started a group called The Other Disappeared to look into missing persons cases going back to 2008.
The cab driver said that many families had contacted him to talk about relatives who had gone missing.
The group met every Sunday to search in the surrounding hills and landscape for the remains of people they knew who had vanished.
In an interview with the Los Angeles Times, one of Jimenez Blanco's friends, Mario Vergara, whose brother went missing last year, said that he inspired many people.
"He taught us how to search and how to push and every day he would give us the energy to carry on."
Jiménez spoke to CNNMexico just the previous week that more than 100 bodies had been found in hidden graves in the area since October, criticising what he said was a worsening security situation.
"We left it clean and now again there are bad people here, but we have to do something, because I cannot leave this to my children," he told CNNMexico. "If something happens to one of my children I will never forgive myself."