The shootout left four people dead, but that was just the beginning. As dust began to settle on a ranch in north-eastern Mexico, thought to have been owned by one of the world's most powerful drug cartels, the battle-hardened Marines stumbled upon their first decomposing corpse.

Minutes later, they found a second, then a third. By the time troops had finished searching the remote property, roughly 90 miles from the US border, a total of 72 contorted bodies had been laid out in rows beneath the summer sunshine. The 54 men and 18 women had all been recently murdered.

A lone wounded survivor, who was left for dead but later stumbled upon a military checkpoint, told local newspapers yesterday that he and the victims were illegal migrants from Central America trying to make their way to the US. They had been taken hostage by the Zetas, a gang of drug-runners who have recently taken to kidnapping and human trafficking. The Ecuadorian man said his group was taken to a ranch by gunmen and shot after they refused to pay ransoms.

Mexico: bleeding to death in the war on drugs

Another 72 corpses found in a new mass grave. Feuding cartels blamed for displays of mutilated bodies. Death toll in four-year crackdown passes 28,000

By Guy Adams in Los Angeles