The discovery in April of 272 bodies in 35 clandestine grave sites in three states — Tamaulipas, Durango and Sinaloa — indicates that the toll attributable directly or indirectly to the violent acts of drug cartels is considerably higher than what anyone had imagined. Like the previous discovery of a mass grave in Tamaulipas, some of the recent killings have been attributed to Los Zetas, but it seems that not all of the victims were US-bound illegal migrants.

It started in the first week of April, when an army unit, investigating a report of a large number of people who had disappeared after having been abducted in March from a bus on the Victoria-Matamoros at the height of San Fernando, Tamaulipas — the same municipality where the bodies of 72 illegal migrants were found in clandestine graves last August — found a grave with 43 bodies. By 7 April the number of clandestine graves discovered had risen to 10, and the bodies to 72.

Between 10 and 12 April another four mass graves were found, containing 50 bodies, raising the total which the state's public prosecution service said ‘might also be related' to the investigation into the abduction of passengers going through San Fernando.

These, however were not the only clandestine burial grounds found by investigators. On 8 April they had located another 12, containing 23 bodies; on 14 April another three, with 21 bodies; on 15 April two more, with five bodies; on 19 April a further three, with six bodies. This second set, which raised the total of clandestinely buried bodies to 177, was not considered related to the abduction of bus passengers.

The investigations in San Fernando had clearly been guided by ‘information received'. As early as 1 April, the army had arrested nine suspects; on 6 April, another five; by 12 April, two more. Then, on 13 April, the federal chief prosecutor's office, PGR, reported that 16 officers of the municipal police force had been arrested in San Fernando, on suspicion of complicity in the killings. The PGR also said that arrest warrants had been issued for four more persons, considered leaders of the Los Zetas cartel in Tamaulipas; rewards totalling US$2.4m have been offered for information leading to their capture. Since last year the municipality of San Fernando has been in the grip of Los Zetas.

By 19 April the number of detainees placed under ‘preventive arrest' had risen to 64; the 16 police officers and 39 suspected members of Los Zetas. These arrests had been linked to 145 of the 177 killings. Nine of the arrests were made in the state capital, Ciudad Victoria.

Tamaulipas was not the only state where clandestine graves were turning up.  In Durango City, ‘information received' led federal and state police on 4 April to a site where 26 bodies were found, clearly interred long before those uncovered in San Fernando. Further excavations led to the discovery of 78 more bodies, across two separate sites in the state capital. On 12 April a farmer in Ahome, Sinaloa, led police to one he found on his land, which contained 11 bodies.

More than 200 people turned up and the headquarters of the forensic service in Matamoros, in the hope of determining whether disappeared relatives were among the disinterred. They came from several municipalities in Tamaulipas and nearby Chihuahua and San Luis Potosí, as well as from states further south, such as Oaxaca and Chiapas.