Authorities across the country are known to work in tandem with organized crime, and it is likely that the local police were involved in or at least had knowledge of all four young men’s disappearances, according to Sofia de Robina, a lawyer for Ms. Herrera.
In 2011, on one of her trips to follow up with the authorities on the fate of her sons, Ms. Herrera came across a growing protest movement founded by the Mexican poet Javier Sicilia, after his son and six other young men were killed by gang members. Called the Movement for Peace With Justice and Dignity, Mr. Sicilia led caravans across Mexico calling for an end to violence.
Ms. Herrera went and spoke to a rally in the city of Morelia, taking with her laminated photos of her four missing sons.
“I heard a harrowing cry when they yelled: ‘You’re not alone, you’re not alone,’” Ms. Herrera said. “In that cry I felt a kind of strength, and I joined the caravan.”
She traveled the country for two weeks, including to Guerrero and Veracruz. But though she found no sign of her sons, she did find something else: dozens of other mothers, brothers, sisters and sons with missing relatives.
“It was something very, very cruel for me to discover that it wasn’t just me,” Ms. Herrera said. “And from there, we started to share that pain, to share that energy, all this anger, all this suffering, to know each other and scream as one.”
But solidarity alone could get them only so far.
Ms. Herrera realized all those parents needed more resources and the knowledge of how to look for their missing children. So she began convincing universities to give workshops on how to search for missing people, the majority of whom are presumed to be killed and buried in unidentified graves.