A Mexican man known as "The Stew Maker" has confessed to dissolving the bodies of 300 drug-war rivals with corrosive chemicals.
Santiago Meza, who was arrested with three other people on Thursday, told journalists that over a period of 10 years he did away with bodies in industrial drums in a village outside the violent city of Tijuana.
More than 700 people died in Tijuana last year as rival gangs fought for control of the city's lucrative drug trade. Many others are missing and believed dead after being abducted.
The drug war claimed 5700 lives across Mexico last year, more than double the number of victims in 2007.
Meza, who was paraded before the media by the army on Friday, said he was paid $US600 a week by a breakaway faction of the Arellano Felix cartel to dispose of slain rivals with caustic soda, a highly corrosive substance.
A high-ranking army officer believes Meza is telling the truth. Police have previously recovered human remains burned with acid in and around Tijuana.
