‘Grief is the end of loneliness”, Cristina Rivera Garza writes in her book, Liliana’s Invincible Summer, which this week won the Pulitzer prize for memoir. For the Mexican author and academic, publishing the book meant sharing the weight of a long-held grief with other shoulders across the world for the first time. Rivera Garza’s sister, Liliana, was murdered by her ex-boyfriend in 1990 in Mexico, where 10 women are lost to femicide every day. The perpetrators are very rarely brought to justice. In Liliana’s case, corrupt police demanded a bribe her father could not afford to continue investigating, and officials immediately referred to the murdered woman as if she had brought on her own death.

For nearly 30 years, Rivera Garza could not manage to say her sister’s name; now, the name ripples across the lips of many thousands of readers, themselves now experiencing that same “end of loneliness” through the perpetual companionship of Liliana, a 20-year-old architecture student murdered in cold blood in her own apartment by a man who was never caught.

“I don’t believe in the therapeutic effects of writing … I really think that the only healing possible will be through justice,” Rivera Garza said. But something she was not expecting was “how readers’ embrace of Liliana and her story played a massively important role in generating a public mourning that was all about companionship and solidarity.”

In fact, it was a reader who sent Rivera Garza a tip after the book was published, leading her to the man she suspects murdered her sister. This man had escaped to the US and lived for years in southern California under an alias before dying in 2020. The reader sent Rivera Garza a link to a digital wake held for him, where people had left messages with condolences using his birth surname. But Rivera Garza is still waiting for US and Mexican authorities to confirm his identity. Even winning a Pulitzer is not enough to move the levers of bureaucracy.

In discovering the life story of her sister’s killer – in particular finding that dozens of friends and relatives in Mexico knew where he was and interacted with him for decades without revealing his location – Rivera Garza was once again confronted with the saturation of machismo in Mexico, a culture that protects violent men and silences thousands of people made victims by their crimes.

Even Rivera Garza found herself paralysed by this familiar silence, both in seeking justice and in documenting her sister’s story. She chose to write the book simultaneously in Spanish and English, using her second language as an emotional buffer while writing particularly painful sections.

The book, which documents Liliana’s final years in the late 80s as well as Rivera Garza’s attempt to find her police case file 29 years later, includes lengthy excerpts of letters and poems written by Liliana before her death, as well as the vivid memories of her friends. In so many ways, Liliana shares the Pulitzer with her sister, her idiosyncratic, wandering prose style, dotted with open-ended, adolescent questions about life and love, proving foundational to the work. Most of these artefacts, which Rivera Garza calls the “effective archive”, were left untouched in boxes in her parents’ home for decades. When she opened them, Rivera Garza said “I felt like I was touching her directly.”

Despite its specificity, Liliana’s story transcends itself, her footprints accompanied by those of thousands of other women who have lost their lives to abusive men. While visiting Mexico City searching for the case file in 2019, Rivera Garza was inspired by the fervour of Mexican feminists who sought justice for their friends and relatives killed by intimate partners. These cases seemed almost indistinguishable from Liliana’s. “The chants vary little around the world, rumbling from mouth to mouth, from fist to fist, across a common sky,” Rivera Garza writes in Liliana’s Invincible Summer.

Though feminist movements have grown exponentially in Mexico in the past 30 years, prompting the official designation of femicide as a crime separate from homicide in 2015, femicides remain glaringly ubiquitous. Combatting femicide, and achieving the justice and freedom from abuse that she and thousands of others crave, will require adopting the terminology created by feminist movements, and using it every day, Rivera Garza says. “This is the only way in which it will become inseparable from us.”

“We are not speaking of gender violence as something extraordinary that happens for unknown reasons. We’re talking about a violence that is structural, that we can identify,” she said. “And of course, the powers that be are not going to be welcoming of this language.”

Though Rivera Garza views her work as defying a state that condones a war against women, she is realistic about the limits of the written word to spark structural change. Even in her sister’s high-profile case, the Mexican justice system, through the Mexico City attorney general’s office, has refused to produce the relevant documents to close the case once and for all.

“They have not done anything about a case that is highly publicised, that’s winning a Pulitzer prize,” Rivera Garza said. One can only imagine the fates of the documents that pertain to the thousands of other, less public femicides in Mexico. “It’s been over two years and they haven’t even called me … essentially I believe that they have done nothing.”

• Liliana’s Invincible Summer: A Sister’s Search for Justice by Cristina Rivera Garza is published by Bloomsbury (£10.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply