Mexico City is a grand old town. Its magnificent central square, the Zócalo, built out of the destruction of an earlier civilisation, is sinking slowly into the marshes from which it had once been claimed. A similar process has now all but buried free expression: Mexico has the dubious distinction of being tied for first place with Pakistan as the world's deadliest country for journalists.
In Britain we worry about the chilling effect of the over-regulation of the press: in Mexico they cut to the chase and shoot (or decapitate) the messenger. Since 2000, 67 Mexican journalists have been killed – a number that President Calderón's war on drugs has only helped to increase. In 90% of these cases, no one has been prosecuted, never mind convicted. Which is why I was there. I was part of a PEN International delegation that, in collaboration with Mexican PEN, aimed to draw worldwide attention to the culture of impunity that silences not only the people who speak out, but the word itself.
The trip turned out to be an eye-opener, revealing the way in which competing drug cartels, inept or corrupt government, the police and terrified media join together in the suppression of free expression. We met politicians and prosecutors, writers and journalists, ambassadors and NGOs, our visit culminating in a public event, "PEN Protesta", where dozens of Mexican writers gave eloquent insight into their country's malaise. The tone was set by one of the first speakers who, paraphrasing Mandelstam, told us that "if you kill poets it means you don't respect poetry but if you kill journalists you don't respect society." Mexico, said another, is a country that "vomits blood"; a third described it as "a magical country full of assassinated people and no apparent assassins". It's a country where, according to one of Mexico's pre-eminent writers, Elena Poniatowska, "reporters are hunted like rabbits."
After the event, I was left with a lasting image of the diminutive, red-clad Poniatowska. While we drank tequila from champagne glasses, she posed for photographs with a lineup of members of the Banda de Tlayacapan. The band was a mixed bunch – women in poncho-topped long dresses, old men and boys, their faces almost drowned by large brimmed hats – and their sound that of strident Mexican brass, strangely slowed. "It's a dirge," the novelist Jennifer Clement explained. "They play at funerals. Seemed right, given we are holding a wake for free expression."
Mentions of funerals were on many lips. Journalists spoke movingly about the loss of their friends and colleagues and of a resulting powerlessness so intense that all they could do was bury their dead. Mexico City itself is relatively safe but at least once a week organisations that protect journalists are asked to hide people from other parts of the country for whom the threats have grown particularly serious. And not only are journalists kidnapped: so are their stories. Airports are turned into information black holes as stories disappear into them.
Asked what could be done to help, the requests became eerily familiar: journalists need training in their craft, various people told us, but more than anything they need training in how to protect themselves. Despite the appointment of a special prosecutor to protect journalists, impunity continues almost completely unchallenged. Of the 55 indictments brought by the special prosecutor to the federal courts, only five cases have been allowed to proceed, and from these, not a single person has yet been convicted. It's almost as bad for community radio practitioners who act as the voice of social movements: they are continually harassed or charged with using the airwaves without a licence, and the law has been designed to prevent them from procuring the advertising revenues that might make them even half solvent.
Clement, who is also president of Mexican PEN, had kicked off PEN Protesta by saying that "words are the rocks we throw at each other". By the end of my trip I understood what she meant. For when it comes to the practice of journalism, and to the prosecution of the murderers of journalists, Mexico is caught in a series of interlocking catch-22s. The government blames the deaths on organised crime. But, according to the London-based free expression group Article 19, up to 70% of aggressions against the media are government-inspired. Most of these can be laid at the door of local and regional government, about which the national government says it can do little. Added to this, an inept or corrupted police force joins with a similarly corrupted media to portray the murders as crimes of passion, which means they are never properly investigated.
The big media corporations often lead the charge in denigrating murdered journalists, even accusing them of being linked to the same cartels they were trying to denounce. This obliteration of a free press is not surprising: when a cartel targets a town for take-over it first compromises the mayor with threats or money and then it takes care of the police. Having taken control, it cannot let the press talk about the extent of its corruption and so has to move in on this, the third leg of the stool.
"There is silence in our country," we were told, "and it is the silence of death." Yet even now, courageous journalists risk speaking out. As I flew back to a freezing London, I realised how brave they are and also how much my visit reinforced my belief in the importance of a free press not just for journalists but for a whole society.
• Gillian Slovo is the president of English PEN.