Reputed leader of Los Zetas cartel in Mexico 's Gulf state reportedly in gunbattle . Arellano Dominguez dies in firefight with authorities , attorney general says . Originally formed as the Gulf drug cartel 's enforcement wing , the Zetas increasingly have branched out on their own . Mexico considered thousands of Los Zetas 's most advanced and violent drug cartels .
Reputed leader of Los Zetas cartel in Mexico 's Gulf state reportedly in gunbattle . Arellano Dominguez dies in firefight with authorities , attorney general says . Mexico considered thousands of Los Zetas 's most advanced and violent drug cartels .