Mexican police say a suspected drug cartel leader they arrested last week has confessed to ordering the killing of 1,500 people in northern Chihuahua state.
Jose Antonio Acosta Hernandez is also a suspect in the murder of a United States consulate employee last year near a border crossing in Ciudad Juarez.
Felipe Calderon, the Mexican president, said on Sunday that the capture was "the biggest blow" to organised crime in Ciudad Juarez since he first sent about 5,000 federal police personnel to the city in April 2010 in a bid to curb violence in one of the world's most dangerous cities.
Acosta, 33, was caught on Friday in the northern city of Chihuahua, said Ramon Pequeno, head of the federal police's anti-drug unit.
The arrest was not confirmed until Sunday, just before Acosta was displayed to the media in Mexico City.