A Mexican woman who doggedly pursued her daughter’s killers in a region plagued by with drug cartel violence [1] has been shot dead in her home, reflecting both the lawlessness plaguing large swaths of the country and the risk faced by victims’ families who pursue justice.

Miriam Rodríguez Martínez was murdered on 10 May, when Mexicans mark Mother’s Day and families of those who have disappeared during the decade-long drug war march to demand action by the authorities.

Rodríguez was shot 12 times on Wednesday morning when gunmen burst into her home in the municipality of San Fernando in the hyperviolent state of Tamaulipas on the Texas border. The region has become the setting for a dispute between rival crime factions [2], which have clashed over lucrative smuggling routes to the United States

After her 14-year-old daughter Karen was abducted in 2012, Rodríguez – like many others who have lost relatives to drug violence – grew frustrated with inaction by the authorities and launched her own investigation [3]. She eventually discovered Karen’s remains, as well as information implicating members of Los Zetas, an ultraviolent cartel formed by former special forces soldiers.

That led to the arrest and imprisonment of the principal suspect in the murder.

Rodríguez subsequently founded a non-governmental group of 600 families who worked together to search for relatives. In the 10 years since the Mexican government declared an all-out war on organised crime, some 200,000 people have been murdered and more than 30,000 reported as disappeared.

Victims’ relatives have often played a key role in the discovery of clandestine mass graves across the country, some of them containing hundreds of bodies.

But such work has often put them at risk of retribution from organised crime groups.

Rodríguez knew she was at risk, and had requested special protection after her daughter’s killer escaped from prison in the state capital Ciudad Victoria. The state government says he was quickly recaptured and that it sent extra police patrols to check on Rodríguez.

“She was a brave person, who worried about others and had the courage of her convictions in her struggle,” said Giovanni Barrios Moreno, whose own son disappeared in 2008 and who is now president of a non-governmental group demanding improved security in Tamaulipas.

“It’s a real demonstration of the non-existent security conditions in Tamaulipas, along with the lack of will on the part of the authorities to provide security,” Barrios said. “Tamaulipas is a failed state, where minimal measures of security do not exist for the population, much less vulnerable groups like social activists.”

Tamaulipas has been long been dominated by the Gulf cartel, but security in the region deteriorated rapidly in 2010 when the cartel’s armed wing – Los Zetas – turned on their masters [4].

In recent weeks, Tamaulipas has been convulsed by a fresh wave of violence after federal forces killed a crime boss known as “Comandante Toro”, leader of the Gulf cartel in the border city of Reynosa.

The Movement for Our Disappeared, a group of families with missing members, said in a statement: “In this dark night of violence and terror that we have experienced for more than a decade in the northeast of the country – and which has unfortunately spread through Mexican territory – is that impunity, the total absence of the rule of law has allowed a system of terror and death as a form of government to come into effect in our states.”

The UN Office of the High Commissioner for Human Rights in Mexico added in a statement: “Beyond their murder, it is imperative to address the structural factors that have placed the families of disappeared persons in a grave situation of vulnerability.”

Tamaulipas governor Francisco García Cabeza de Vaca said on Twitter that the state government “will not allow the death of Miriam Rodríguez to be one statistic more”.

But many Mexicans also expressed outrage that the country’s president, Enrique Peña Nieto, failed to comment on the murder, instead responding multiple times to a tweet from actor Leonardo DiCaprio demanding protection for an endangered porpoise species known as the vaquita marina.

David Agren in Mexico City