Few people have done more to get to the truth of the case of Mexico’s 43 missing students than the investigative journalist Anabel Hernández.

The incident is arguably the most notorious in Mexico’s recent history. On the night of 26 September 2014, students from the Ayotzinapa rural teacher’s college in the south-western state of Guerrero commandeered a bus in the town of Iguala and set out to attend an event in Mexico City. They never arrived. Along the way, they were violently attacked. Six were found dead, dozens injured and 43 of them simply disappeared.

Hernández began investigating within the first few months of the attack, laying out her findings in her book, La Verdadera Noche de Iguala (The True Night of Iguala), released in Mexico in 2016. Her findings were shocking: where the government had said they knew nothing about the attack and the students’ disappearance until well after it had taken place, Hernández found that federal authorities had been monitoring the students for four hours before it happened. The drug cartel, the army, intelligence services and the federal police all contributed to what happened that night, she argues, and then did everything they could to cover it up.

The English translation of La Verdadera Noche de Iguala, titled A Massacre in Mexico, was released last October. This week, the Mexican journalist will appear at the Sydney writers’ festival to speak about the threats to journalists around the world.

Hernández’s tale is one of the most banal kinds of evil – officials lying under oath, money laundering – coupled with the most horrific: torture, forced confessions, rigged trials. Hernández says she wants the book to show people the true face of government, police and army corruption in states that are supposedly democratic.

“The problem is that when we talk about these kind of things it is like corruption is something you cannot touch,” she tells Guardian Australia over Skype. There is, she argues, a sense within the global news media and its consumers that corruption is a kind of victim-free crime. The 43 disappeared students prove otherwise.

Mexican journalist Anabel Hernández. Photograph: SWF

“People might think that journalists like me are exaggerating, that corruption makes some people more rich and nothing worse than that,” she says. “[But] this book shows how corruption can kill. How corruption can disappear and torture people. How it can hurt a country like Mexico.”

In chronicling the murder, torture and disappearance of innocent young people and witnesses, A Massacre in Mexico also reveals the extent of what Hernández calls Mexico’s “political decomposition” into a society ruled by a culture of corruption and impunity.

“Forty thousand people have been disappeared in Mexico in the last 12 years,” Hernández says. “One quarter of a million people – children, women, good men – have been murdered. This is the product of corruption.”

Hernández’s revelations had a profound effect on the Mexican public. The Ayotzinapa case became a flashpoint for last year’s federal election. Millions switched their votes from the long-standing dictatorial Party of the Institutional Revolution to Andrés Manuel López Obrador’s populist Morena party on the promise that this emblematic case of the violent and unaccountable conflict that plagues Mexico might be resolved, making way for a new dawn of peace, transparency and the rule of law.

Since Hernández’s research into the Ayotzinapa case first began to be published in Mexico’s weekly magazine Proceso in 2014, both the Inter-American Commission on Human Rights and the United Nations have come to similar conclusions about what really happened that night in Iguala. Under López Obrador’s administration, the official investigation into the case has been reopened. The president has overseen the establishment of a “truth commission” into the fate of the 43 missing students and promised an exhaustive effort to find out what happened to them. He has also promised an end to the corruption of Mexico’s previous administrations and collusion with organised crime.

It’s not about ‘crazy Mexicans’. This corruption can destroy every country Anabel Hernández

These are bold commitments. But after all the horrors she’s uncovered throughout her journalism career in Mexico, Hernández is understandably sceptical.

“In his election campaign [Obrador] said there would be an amnesty for the cartels; that he would not prosecute the narcos and he’d be all peace and love,” she says. Indeed, shortly after his election in July, Obrador said he planned to fight drug cartels with “hugs, not bullets”. But these warm words from the new president contrast sharply with the release of data showing that the first quarter of this year was the most violent in recent Mexican history, with a total of 8,493 people killed.

“You can’t think that just because you say things will change, that they will because you want [them] to,” says Hernández wryly. She no longer lives in Mexico. The journalist and her family moved abroad for their own safety: by the time they left, the death threats were constant.

People outside of Mexico might hear the stories she tells and think “Oh yes, these Mexicans, they’re crazy”, she says. “It’s not about ‘crazy Mexicans’. This corruption can destroy every country.”

Australia in particular should remember that the drug cartels she has investigated have a presence there too, she says. “Every country where these cartels are able to penetrate could have these problems. Wherever they have penetrated, somebody has opened the door.”

• Anabel Hernández is speaking at the Sydney writers’ festival on Thursday 2 May and Sunday 5 May