Police say they have arrested the 'mastermind' of the Monterrey casino arson...that killed 52 people in August...and outraged Mexico.
Baltasar Saucedo Estrada...aka "dog-killer"/Mataperros...is the alleged local leader of Los Zetas narcos.
So far...20 suspects in the deadly fire have been arrested.
Saucedo Estrada carried a $ 1 million bounty for his capture.