OFFICIALLY, nearly 35,000 people have been killed since Mexico's president, Felipe Calderón, began an assault on his country's drug-trafficking “cartels” at the end of 2006. But the true body count will never be known. On April 6th police discovered mass graves near San Fernando, a town in Tamaulipas state near the border with the United States, which so far have yielded 183 bodies. Two weeks later hidden tombs were discovered in the north-western city of Durango from which 100 corpses have so far been extracted.

The Tamaulipas victims were apparently killed with sledgehammers or burned alive. They included a car salesman, a social worker and a Guatemalan migrant. Investigators believe they were kidnapped from buses to be robbed and raped by the Zetas cartel. The authorities' failure to stop the slaughter, even as unclaimed luggage mounted at bus terminals, is stunning: only last summer, 72 migrants were found murdered near San Fernando, supposedly by the same cartel. However, police did free two groups of kidnapped migrants elsewhere in the state this month.

Explore our interactive map of Mexico's drug traffic routes, "cartel" areas and crime-related homicides

The killings undermine the government's claim that drug-war casualties are almost all criminals. Mexicans are tiring of this war without end. On April 6th there were protest marches in 21 states, following the suffocation with duct tape of seven youths in the formerly quiet city of Cuernavaca. Polls shows that for the first time under Mr Calderón worries about security trump those about the economy. Although cartel henchmen continue to fall—11 middle-ranking Zetas have been killed or captured this year—there is no shortage of new recruits. La Familia Michoacana, a gang that was virtually destroyed in January, announced its rebirth as the “Knights Templar” in March. From the ruins of the Beltrán Leyva cartel, smashed last year, have sprung two new upstarts.

Some analysts say the plague of kidnapping (up fourfold compared with 2005) and extortion may show that government pressure is forcing some drug cartels to diversify. Organised crime in the region has never been only about drugs: as well as cargo theft, prostitution and the like, the Sinaloa mob is said to have interests in avocados; in El Salvador, a feared “cheese cartel” imports dodgy dairy products from Honduras.

Whoever the perpetrators of these horrors and whatever their motives, they clearly counted on official complicity. Of the 74 people arrested so far in connection with the butchery in Tamaulipas, 17 are local police officers. More than four years after Mr Calderón launched his assault, his government has yet to create a national policing system it can rely on.