FOR almost three years residents of Allende, close to the Mexican border with Texas (see map), harboured a dreadful secret. In 2011 the town of 27,000 people suffered a violent attack by the Zetas, Mexico’s most brutal drug gang. Driven by a thirst for vengeance against two local men whom the gangs believed had betrayed them, mobs of Zetas drove into town, rounded up their extended families and friends—totalling hundreds of people—and abducted them at gunpoint. They then drove bulldozers through their houses, and mortared or set fire to them.

Until this year the barbarity went virtually unreported; there were only dark rumours of what had happened to those who had gone missing. Even though dozens of the gutted houses are dotted like war ruins around the town centre, talk of the incident was suppressed—from fear of, or collusion with, the Zetas. Reynaldo Tapia, who took over as mayor of Allende in January, says two hapless youths who took visitors on a walking tour of the devastated homes were shot dead.

But in February, almost three years after the crimes were committed, federal and state investigators acted at last. On farms near Allende, they found oil drums—known to the Zetas as “kitchens”—where the victims were incinerated after being shot. Reports of the number of bodies found in clandestine burial grounds around the area range from 300-500.

Federal forensic police in Mexico City are still studying the charred remains to determine exactly how many were killed. Mr Tapia says he thinks 30-40 families from Allende, some with as many as ten members, were “exterminated”. He has compiled a list of 34 destroyed houses in the town that he plans soon to demolish, because they are a morbid reminder of a “nightmarish” past. The list includes the names of homeowners whom Mr Tapia can remember going to church with. A few managed to flee to the United States. The rest have never been heard of again.

The massacre may well be one of the worst in Mexico’s six-year drug war from 2006 to 2012, when the previous government sent in the army against drug gangs, setting off murderous turf battles. But it is impossible to know for sure. Uncertainty surrounds the numbers of people who went missing nationwide as a result of drug-related abductions. In 2013, shortly after President Enrique Peña Nieto took office, a government list put the number in 2006-12 at over 26,000. Last month Miguel Ángel Osorio Chong, the interior minister, said the figure had been slashed to 13,000, because many supposedly missing people had been found alive. In the meantime, however, new victims have been added to the total: another 8,000 were unaccounted for in 2012-14, he said.

It is not known whether the tally of 13,000 includes those from Allende. In fact, little has been divulged about who the government’s numbers include, where they are from, what method was used, or whether the missing are believed to have been abducted by organised criminals, by police, or by a combination of the two. Armando Luna, interior minister of Coahuila, Allende’s home state, says in his state alone (just one of 32 in Mexico) there are 1,800 disappeared, the “immense majority” seized against their will.

Yet establishing the number of disappeared is only the first step. Trying to find them is another; prosecuting those responsible another still. Although the government has set up a task force to find the disappeared, human-rights groups say there is little evidence that the data on those missing, including DNA samples of their family members, are being matched with the DNA of unidentified corpses. On June 5th Animal Político, an online news outlet, reported that in the 12 years since a genetic databank was created, it had only been used to identify 542 bodies, even though 26,000 DNA samples have been taken.

Families of the disappeared say the search for their loved ones has been left up to them. Often at great risk, they traipse from morgue to morgue, police station to police station. In May Sandra Luz Hernández, whose son was abducted by armed men two years earlier, became the latest activist to be gunned down. She was apparently lured to her death in the northwestern state of Sinaloa by someone claiming to know her son’s whereabouts.

Part of the problem, the families say, is that the government gives low priority to their cases because they assume many of the victims were criminals themselves. Yet often local police and security forces were allegedly also involved in what are called “forced disappearances”. Nik Steinberg of Human Rights Watch, a New York-based NGO, says it has given the authorities evidence of 40 cases of such abductions (it has scores more). “The bottom line is that they’ve failed to take the basic steps to advance the investigations,” he says.

Some encouraging changes are taking place at local level. As a result of pressure from Fundec, a Coahuila-based church group that acts for the families of the disappeared, last month the state expressly prohibited abductions in its constitution. A new law in Coahuila also allows victims’ families to claim rapid legal recognition of an abduction, which will enable them to get access to bank accounts and claim work-related and social-security benefits owed to their loved ones.

That is unlikely to help people in Allende, who remain too scared to admit to any kinship with the missing. Mr Tapia, the mayor, says in other respects “peace and tranquillity” have returned. On June 9th he held a party for journalists (some with bodyguards) to reinforce that message. He spoiled things somewhat by taking your correspondent to a nearby stream, still festooned with crime-scene tape, to show him where he had once fished out two corpses.